They use hexchat as an example but do these processes run with the users configuration? Wouldn't this leak IRC usernames if you forget to change it.
... Or leak cookies if you launch a browser?
Same thing could have been said about using Tor to login to Gmail (if it were not HTTPS).
IRC seems pretty dangerous if you want to remaining anonymous considering how many people are logging disconnection times allowing them to be correlated with other network disruption events.
Is there a “common name”?
In your example of correlation of connection times, it may not be your goal to remain anonymous from the network and its participants, you may be interested in the location-hiding properties, and/or adversarial networks (like local government or corporate networks) and firewalls.