Am I correct in believing that when the transaction archive shows "cancelled" for a swap that it does not specify WHO did the canceling? (be it requestor, sender, or PBS???)

My Transaction Archive has a pull down menu with "Canceled by Sender" and "Canceled by Requestor" options.  It can be a bit confusing because sometimes you are the Sender and sometimes you are the Requestor.,  It shows the other persons name and PM link as either the TO of the FROM and the basic request details.

If you hover over the red X it will tell you who canceled.

if it is the middle of the night, chances are that the order timed out.  if it was during the day, then it was more likely the "not now" button.