It’s good not to assume, but perhaps this requires no assumptions? The facts are clearly set forth. The reference is to what seems to be a post-maintenance test flights NOT under Part 121. Is this not clear to everyone, or am I way off...?

Who would take an aircraft with a reported vibration — for which there is presumably an open (unresolved) write-up—up on a revenue flight with pax?

Maybe I’m missing something...?