so you mean live chess?, because this is a beta and glitches should be expected, if you mean correspondence chess he could have won another game at the same time.
Some rating systems make it possible for you to gain points even if you lose*
*(provisional ratings, that is)
There are three ratings in live, blitz, long and quick.
All three types of games are in one list so the ratings do not follow a logical pattern.
You are looking at the wrong rating, his rating before the game was 1483, and after the loss it was 1470. If this has happened twice, as you said, I suggest glasses.
There is one more way - when you are playing live with opponent, who are playing several games simultaneously, he can lose and win his other games while still playing with you the same game, and you will see how his rating is jumping in realtime. While jumps not in realtime are obvious, so i presume you was talking about realtime jumps.
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