Boosting. What qualifies as Boosting?

So my team fell "victim" to a high ranking player/streamer playing on a smurf and playing with his viewers/subscribers. He single-handedly carried the game (I afterward was able to identify who it was based on something said in the post-game screen; no one advertised it). I know that this was rather harmless since smurfs exist at every level, and they will eventually get to their appropriate level (just as people who are boosted/carried will fall accordingly). I eventually got on the stream and made a light-hearted "thanks for destroying my team :'(" comment, and he chuckled and apologized. Just him saying that upped my mood, and I understand that people just want to play with others.

I was wondering if this counts as boosting, though, if a player of an obviously higher skill level plays with players of an obviously lower skill level with the intention of carrying them up. Is this punishable? I'm not wishing any ill will for this person since he seemed like a nice guy, but I would like to inform him if it's improper to do so. I wouldn't want him to get in any trouble.

Thanks.