Patriots are interviewing our LB coach for their defense coordinator position

Then why do people consider Josh McDaniels to be from Belichek’s coaching tree?

Honest question.
I think it's a good question. You probably need two trees, one for scheme and one for head coaching. Aaron Glenn would be part of DA's tree for defensive scheme, if he gets promoted to HC then he should be part of Campbell's HC tree (which of course started with Payton, which started with Parcells, etc).

McDaniel would fall under Weis for scheme and Belichick for head coaching.