That just means he wasn't his sole master (ie. Qui Gon to Obi-Wan, Obi-Wan to Anakin). Kavar could still have been his "master" the way Obi-Wan says that Yoda was his master.
From the sounds of it, the Exile went off to fight in the Mandalorian wars because he attained full Jedi Knight status, which indicates that maybe he didn't have a specific master yet, but had many masters who taught large groups. And Kavar (along with Atris) seemed to be hinted as two of those teachers.
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I don't know!
You shall be right... I also think, that Atris and Kavar weren't the only teachers the exile had....