According Psychopathic (challenger tier Nasus player) it's a bug that it doesn't stack.
Plus, here's a bug fix for Tear a while ago:
Bug Fix: Abilities which empower a champion's basic attack will now properly trigger Mana Charge when hitting epic monsters.
Yet, tear no matter what does not work on Nasus Q? Why would it get a bug fix for empowered AA if you can't stack with empowered AA?
Maybe that was before item changes, sure. Why is this line in the wiki then?
Empowered basic attacks gained from abilities will count for triggering Mana Charge upon consuming the attack.
Either way, there's a lack of clarity.
I talked with Psychopathic about this and reported this for him thinking it was a bug, GreaterBelugeWhale (comment above yours) did the investigating and found it to not be a bug because Nasus Q does not trigger ability effects, which is intentional. I do agree there is certainly a lack of clarity around it and similar effects though.