None of the things you say are evidence for it being planned
Why else would the tech have handed him a guitar with the capo on three? When you put a capo on a guitar it affects the tuning very slightly so ideally the tech tunes the guitar with the capo in the place it will be used. The tech handed him a guitar with the capo on three, he knew that’s what Bruce would want for playing the song in G so all the nonsense about which key to do it in was just that, a wind up.
Singers know their vocal range, and how to make the most of it. When Noel Gallagher does Wonderwall he does it a fret higher than when Liam sang it. Whatever he does two frets up. Ozzy does Paranoid in D or E flat now because he can no longer get up to E. In a guitar band it doesn’t matter what key you use, however the keyboard and horn players are not going to be happy if you announce you’re doing the song in E flat rather than E today.
Edit: I doubt the sign was a plant, it was the reaction to a song from his repetoire that was a wind up. All the musicians would have seen it and not flinched, “know that”, but then Bruce started messing about and talking about choosing a key. If I’d been in the band at that point I think I’d have have fallen for it and started mentally transposing my part into each key he announced ‘G’ yeah that’s the usual, ‘A’ Ok that’s A and E and two frets down for the solo – for some of the band it would have been an uncomfortable moment.