Let me use the urban subdivision I am literally currently walking in as I type (not in the QC, but in Lincoln, Nebraska) as a good example of what I mean, to explain both how it might appear walkable, say in a brochure or zillow listing, but actually works to make walking much harder than it needs to be. I say this from the perspective of someone who does in fact walk in this neighborhood; it is not impossible, but it is also not a "walkable neighborhood" in a meaningful way beyond the nare minimum of "you might not die walking here."
1. Recreational paths that are only for recreation
A big offender in false walkability is the existence of multiuse pathways that appear to offer pedestrians, cyclists, etc. privileged access. Ones like this:
It's true, you can't drive here, and so as a pedestrian I am both safe from cars and superficially able to go where they can't go.
But not in a useful way.
This path doesn't actually go anywhere. Oh, it touches a lot of the neighborhood (most houses can access a trail! Yay!) and it intersects parks and sidewalks periodically, so you can indeed use it to go places. But it meanders, and when you actually get close to a destination, it falls short. Here I am next to the local Hy-Vee grocery trying to get on the trail. How would you cross this, from the area I'm walking in to the actual recreational path on the other side?
Well, the answer is walking all the way down there to where the cars cross, and using the sidewalk, because the path doesn't have its own crossing of this tiny patch of water. Or hopping across it and getting your feet wet, like I did...
It's similar elsewhere. There is a path, sure, but it's main use is recreational-only: here is a space you can walk or bike without a car in your way, so you can exercise safely. It's not a path for use; it doesn't make it easier to actually get places. False walkability in practice, because it doesn't actually make walking anywhere in particular easier.
2. Sidewalks aren't good just because they exist
In a similar vein, the sidewalks here are also less useful than they should be. Yes, they exist, and that is indeed a step up from many such places. But they suck, and that matters too.
How do they suck? First, they are narrower than they could and should be, leaving huge gaps I grew up calling the most car-centric possible name: parking strips.
The width of the sidewalk makes it clear only one person should be walking here, not, say, two abreast talking to each other or two or more passing in different directions. That makes it clear in turn that this is not really for walking access; it's for being able to walk to a car or to get the mail or to let a dog do its business.
And when it's inconvenient for cars, or just randomly sometimes, the sidewalk disappears or lacks crucial connections, like across a giant field.
Or a crucial connection across to a mailbox.
These are technically better than no sidewalks at all, and I am glad they are here, but come on.
3. The street plan hates you
In some cases, what I am about to describe could be a good thing. It could be a chance to make the recreational paths do exactly what they don't, and provide unique and pedestrian-friendly access where cars can't go.
This is not that case.
The streets curve and bend and do their best to cul-de-sac without actually being cul-de-sacs (or in some subdivisions but not this one, they actually are). So those sidewalks don't let you go straight to a destination. This might make sense for a street trying to slow down cars or make sure they don't use the subdivision as a passthrough. But for pedestrians, who don't exactly get up to high speeds, this is silly verging on aggressively unproductive.
Again, it gives the potential to cut through those curves to make it easier for pedestrians, and in a place or two we might actually see that:
This friendly path gives easier access to a shopping center, though it does end up dropping you directly in a parking lot anyway.
But by and large, the lost opportunity here of not doing those cuts is what confirms this as false walkability. There was a chance to make the sidewalks and recreational paths a network that actually assists pedestrians and potentially makes walking easier than driving, or at least uniquely beneficial even if cars are still centered. But that opportunity is ignored, and instead we have false walkability: signs and symbols of walkable neighborhoods without the real thing.