It's hard to say he was feeding, unless he is saying it or it's really obvious like he only buys tears and so on.
In this case maybe it was a bad player, maybe he doesn't know how to play anivia it's quite a difficult champion to master...
Anyway you can't punish someone just for being bad.
You should report him for feeding if you think he was doing it, maybe if he does that pretty often he'll get a punishment, but it's hard to prove.
( You can clearly often see people in chat saying that someone is feeding, but more often than not it's someone having a bad game or something like matchup he doesn't know, ...... )