I think it does not help to discuss whether a moderator should or should not fall for a situation that could be avoided by sending user IDs in every IRC message (JOINs, PARTs, subscription messages etc.) in the first place.
This has already been requested multiple times before months ago, especially for the subscription mesage [1, 2], and there unfortunately has not yet been an official statement why this cannot be implemented (as far as I know).
So I’ll try it again here:
Is it possible to have user IDs on JOINs/PARTs and subscription messages etc.? Might it be possible to extend the subscription notification by also sending something like a USERNOTICE (e.g. with msg-id just being sub instead of resub in this case) to match the resubscription notification process? 
[1] How to detect initial subscriptions for people with "special" names
[2] Sub-streak STILL not fixed after 4 months? (last paragraph)