I take responsibility for this - I was the RSO at the time (and I know that you're not calling me out John).
When the rocket was initially presented, the motors listed was "E16". Just that. To which I asked for clarification. On examining the rocket, I noticed that the upper-stage motor was loose in its mooring, and recommended to the owner that they secure it, and clarify the motor designations, to which they seemed unsure. The owner left the line and returned with the suggested fixes and clarifications.
The reason I take responsibility for this is that my intuition was that this was a new flyer that was unsure, which resulted in my first challenge. And I thought that I "saw red" when I looked at the bottom motor setup (this rocket used cellophane tape to wrap the booster and sustainer) to confirm a booster. Obviously, I was confused. *But* it is possible that initially the booster was an E16-0 and was erroneously swapped out when the repairs were made.
Credit to Kenn who engaged the owner and relatives on circumstances of the flight. They felt bad about it and welcomed the discussion. I spoke with the folks afterwards, and it turned out that they had never flown a multi-stage rocket (I suspect now that this was the first build/flight for them). I suggested that they start with a small multistage model and work up from there.
What catches my attention here is that I missed the 3600' altitude prediction (which I would challenge*). I just assumed that they would never see the sustainer when I asked if they really wanted to do this, which was negligent on my part. Then again, I'll often let a BT-20 fly on a C6-7 motor, assuming that it won't come back, which as I write, also seems wrong.
* I couldn't help myself, went to the Apogee website, and downloaded the Rocksim file for this rocket. On a clean build (which the rocket in question was not), an E16-0/E16-8 combo sims at 2492' - still too high to Claude's point. The other thing to note is that the rocket sims as overstable, which would present a weathercock situtation. I'm not recalling the winds for this launch.
I also scrutinized the parts list and verified what I suspected when presented with the rocket - that initially the motor mount in the sustainer was loose.