The name of the show is a play on the DnD feature of rolling a critical. Seems a bit unfair to criticize someone else borrowing a classic DnD term just because Critical Role got so popular.
Again, this is not a legal analysis. This is a decency analysis.
I might be more simpathetic with their naming choice if it would have been an accidental thing. It could be that the makers of critical-notes never heard of the brand Critical Role, they just settled on the same word because of the game term. This is unlikely to be the case. Critical notes mention on their frontpage that they support the Exandrian calendar for note taking. Exandria, and thus the exandrian calendar, is the invention of Critical Role’s Dungeon Master. The chance that they heard about Exandria but haven’t heard about Critical Role is basically zero.