Functionally no, it's not DLC, but I'm not really interested in debating semantics. I simply mean it's extra content which is not in any way required; it's an extra reward for people who bought the Amiibos. It's not too dissimilar to pre-order bonuses and the like.
You may not like the concept of Day 1 DLC (I'm neither here nor there, personally), but its mere existence doesn't give him a moral right to just straight up pirate the next game in the series. If he felt that he NEEDED those Amiibo bonuses, if we're in a world of "eye for an eye", he could/should have done as I said and bought a re-programmable NFC card and gotten the things he felt he'd been cheated out of for basically free. Not stolen their entire next game.