Technically, is using a touchscreen considered cheating?

On the mobile version, no! However, using a touchscreen on the web or steam version would count as an emulator, which is cheating. Take my thought with a grain of salt tho, cuz im not a mod

That's exactly that but it will not be considered "emulator" but just An unfair advantage. So if you want to play with touchscreen, play the mobile version :)