If I transfer a stress token to T-70 Nien Numb with Amilyn Holdo crew, does that "transfer" count as "gaining a stress" for the purposes of Nien Numb's pilot ability?

Thank You

Yes.

Yep.

From pg 19

Quote

When a ship is instructed to transfer a token to another ship, it is removed from that ship and assigned to the other ship.

◊ If a ship involved in a transfer is not able to remove or gain the token involved, the transfer cannot take place.