That's exactly it. I've never used GSX before, I just started noticing this happening seemingly randomly on VATSIM, some airliners push back normally, some have their nose up in the air. I queried the VATSIM subreddit and forum, as well as various MSFS forums, and most people pointed at it being "someone using GSX for their pushback". I started asking directly via VATSIM message whether they used GSX, and the answer was always yes. Then switching over to try X-Plane (and of course an entirely different VATSIM client), the exact same thing was happening.
I feel that somehow when GSX loads the nose wheel onto the tug, the height of the nosewheel is being translated as feet and not inches. It's no huge deal, but when you have these photo realistic airports and liveries, seeing these silly pushbacks kind of throws cold water on the immersion factor. So whatever the cause, it would be awesome if it was fixed.