Not sure if it is real reflow, doesn't seem warm enough. Maybe some contact point was not optimal, and by heating everything and the expansion resulting from it there was some repositioning causing the contact to work properly again. I'm assuming this because we had a similar, but inverse situation once. There was a small soldering problem that would only manifest after the PCBs got heated >50C.

But in the end it all comes down to luck, it's not like 'heat it' is the new tool that will fix all. (My MBP had a swollen battery, wouldn't dare putting that thing in an oven)