Possibly but maybe he didn't.While this is true, it wouldn't hurt to look into the culture and customs of a country you're visiting simply for the fact that something that is perfectly acceptable in your own country may not be in another, and that goes for anything really not just for sports spectating.
Always better to be safe than sorry.
Taking it one step further, I'm sure many people on here have clapped an opposition goal at some point when it was a screamer (andros Townsend a few year back springs to mind) or a legendary player being subbed off and that wouldn't be seen as being bad etiquette even though it's directly clapping the opposition.
Salah could have scored the greatest goal ever and none of the 'traditional' city fans would clap but would an American at his first game know when it's acceptable to clap the opposition and when it's not?