I agree it's a poor look, especially if the "exec" in the airbridge didn't share the full reason for bumping. I'm sure they have their own reasons for not sharing more, but in the end it's not good and evidently as demonstrated by this thread it leaves customers wanting answers.
I've been moved from a preselected Business seat to another Business seat on a QF A330 before with no explanation before, only to see a likely staff member sitting at my old seat (based on their long conversations with the CSM). The most logical explanation would be that the other seat was broken (as is unfortunately somewhat common with those QF J seats) and they put a person on staff travel there instead. However, it left me wondering and I'm sure some customers would not have been happy with the sudden seat move. It would've been very easy to just tell the passenger why they were moved, but for some reason they don't.
I suppose you could interpret this as they have something to hide (a reason for moving me for staff that I wouldn't like to hear), but I doubt that.
As for why OP was bumped, I feel like Occam's razor should apply here. If the CSM said it was "techs", then it was probably Qantas staff of some sort. I suspect we'll never know if they're tech crew (pilots) or aircraft technicians or whatever. Maybe someone misread or misheard something hence the switch from referring to them as pilots to not.
In theory, could it have been all a lie to cover up for something else (a staff member doing a favour for themselves or someone else etc.)? Yeah, sure. However, I just don't think that passes the pub test, especially in a large organization like Qantas.
As an aside: I do miss the days of the Red Roo account, as they could've usually looked up the flight and given a straight answer immediately, instead of generating 7 pages of speculation.
@Pushka I'm most curious if you've gotten a refund for your upgrade yet. Knowing Qantas, I know the answer is most likely not. For an involuntary downgrade I would hope you get your points back plus another nominal number of points for "Compliments of Customer Contact" or whatever.