Yes, on a BGA the pads are under the IC package. That BGA will be on a PCB close to other ICs which has other packages. Using a hot airgun risks distributing small balls of solder.
If you can accidentally create solder-bridges with a hot-air rework, then there was too much solder; even if you're talking about fine-pitch TQFP's. I've accidentally made bridges using QFN's but only on crappy homemade PCB's and again, with too much solder. It is usually easy to correct. You can dislodge nearby capacitors, diodes, resistors, etc. but that's about it.
On a good PCB that's been cleaned properly there won't be any errant solder-balls, and surface tension will not allow them to form even when using a hot-air gun or rework tool. I've never seen a hot-air tool that blows with enough force to overcome the surface tension of the solder.
I have managed to get make a mess with solder when removing IC's using compressed air (not for the faint of heart), but that's a different story and it is still easy to clean up.
You're talking about people who know what they're doing, using correct hot air rework tools.
I'm talking about people who don't know what they're doing using paint-stripper style hot air guns.
I have seen faulty PCBs caused by people using that style of hot air gun to rework devices. I used to have photographs but don't have them any longer, but there should be photos in some of the "soldering problems" engineering books.
