alt Hacker NewsFair point. My understanding is that the Senate "assumes" a quorum unless someone suggests there is not. Since it was AFAIK around 2am... my guess is not and they all just wanted to get the heck out of there. Since no recorded vote we may never know. So I stand corrected on the number.
Your understanding is correct. The quorum call has a priority and can be done by any member.
The session has to start with a quorum and it's assumed that there is still a quorum since nobody has done a quorum call.
I have to assume that if someone actually objected to this, they would have done a quorum call before leaving the session. That or the few objectors simply left early not thinking this would go to 2am. Though, they could have always came back. They almost certainly would have had staffers there who'd inform them that something like this was coming up.