I don’t think pokemon heights are, like, the size of the sprite, per say. I know the label is “Height:”, but I don’t think it’s really that simple.
Say you have a snake Pokemon, like seviper. Is its height as seen in its sprite pose really 8'10"? No, it’s a snake and if it wasn’t posing it’d probably be pretty “short”, height-wise. So 8'10" is probably how long it is, because that’s how you generally measure snakes in real life.
Even quadrupedal pokemon, their heights probably aren’t the entirety of their sprite. As far as I’m aware, animals like dogs and horses are usually measured to their shoulder height, not head height, since they could droop their head or hold it high, which would change their height drastically. So a rapidash isn’t 5'07" tall as seen in its sprite, it’s 5'07" tall to the shoulder, which means it’s actually taller than you’d expect from the listed height.
Bird and bat Pokemon are probably measured by wingspan. What sounds more likely, a crobat that’s 5'11" tall, or a crobat with a 5'11" wingspan? And fish are usually measured in length, so fish pokemon would also be measured in length, not height.
I would say humanoid and other bipedal pokemon are Actually measured by height, but probably just to the top of the head. The height probably doesn’t count crests, like on gallade and bisharp, or ears, like on lopunny and lucario.
Pokemon that don’t follow the anatomy of Common Animals™ would be measured differently from case to case. Electrode would have a diameter of 3'11", honedge would have a blade length of 2'07", etc
Also, I would say the listed “Height” is probably just an average of the species. Heights between individuals of most species can almost certainly vary from each other by at least several inches.