Learning: Smurfing

So I was in a game, we lost, and aside from a higly angry ADC it was not a bad experence. No real toxicity aside from bot, and at end of the game there was the normal trash talk.

No issue with any of this, learning experence, right?

Then their jungler began digging into me, saying refund my skin, and that he was a gold smurf and that I (and my team) were garbage/rank shame ect. He posted his accounts, and there is very little question that its the same guy (names almost identical). The account he was on however had a 20% winrate, with things like Soraka jungle, with one of the games he won being an 0/8 udyr. This account is clearly being played to lose, to troll, and so I put that off to Riot to deal with.

What I want to know is this: What is acceptable for smurfing? I ask because I have a "smurf" account- an accound I am ok dodging games with- and my main one, and thats the only real difference. I play to win every game. Accounts/smurfs like this, how common are these and does the community endorse/encourage it?