Thanks a lot for picking this up!
I noticed a strange thing about the recording that Shirai deleted. When he stops the recording, the counter is at 01:42.70 (one minute 42.7 seconds, it is definitely not one hour 42 minutes). Quite a bit too short to be a recording of them at the bar.
There are several possibilities, but I like the one where Ishidaira remote controls his phone via AirDroid or something similar, has been listening in the whole time and starts a new recording when there is only the two of them left. Which means the earlier recording is safe.
Of course the most likely (and boring) explanation is that the mangaka just put in the picture of a phone recording and didn't bother to change the counter