Yes, I am 90% sure this was the cause - though as you know, we are forced to guess!
Discussion
But given you're somewhat not new to coinjoin, were prior bookings not private UTXOs?
Bit too much, prefer not to say more.
Bitcoin onchain has zero privacy. The coinjoin only sort of resets the pseudonymity, but all the details are there, which is how they know you did it.
Just use lightning in this case (for anyone reading, for the OP it's too late, SFYL)