My question is about something that happens in S2E98 of Critical Role (potential spoilers if you haven't watched it yet).
In the episode, the wizard attempts to counterspell a dimension door spell. The counterspell is 4th-level just like dimension door normally is; however, the DM mentions that because the caster of dimension door is a warlock, it is a 5th-level dimension door spell, and the wizard still has to make the spellcasting ability check to see if counterspell works.
Is there some official rule that would explain why counterspelling a warlock would be different? This could of course be some house rule, but I don't see any hints that this show would have such a house rule.
The warlock is an NPC; his eldritch blast gives 3 shots, so he's at least 11th level. The player characters' party is 11th level.