1. The email they sent out didn't specify whether your account was included in the 5% of compromised users, or whether you had linked GitHub or BitBucket accounts that they unlinked. The only way to know seems to be if you still have a linked GH/BB account then you're (probably?) ok.
2. They mention you should "check security logs to see if any unexpected actions have taken place" and linked to GH/BB security audit log pages, but I don't believe that's sufficient, you also need to check for rogue commits.
3. They haven't said when the breach occurred, so there's no way of knowing how far back to look. They "discovered" it on Thursday, and say it was a "brief period", but that's meaningless.
4. They downplayed it as "brief", "non-financial user data", and "less than 5%" of users. I care more about the integrity of source code and builds than any financial information I might have given to Docker.
I can sometimes forgive companies for breaches like this, if they own up to it and do an excellent job of communicating what happened, how, when, what the impact and mitigations are, both internally and for their customers. That was not the case here.
EDIT: they discovered the breach Thursday, but still haven't given a timeframe for when it may have first occurred.