Via https://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html ...

From section 3, my understanding is that if you distribute then you must do one of the following: a) include complete source code b) include an offer of source code if contacted c) include the offer of source code you originally received

(It's a bit more complicated than that... but close enough)

So... if they're distributing the kernel as part of a drone they're selling, these clauses would apply?

I'm not sure why "changes" they may or may not have made would have anything to do with it?