Dānlín and Jonathan Lee are obviously playing table tennis. Why is it called singles instead of doubles?

That is to say, you challenge your opponent alone, so it's called singles, not the sum of the number of times two people fight. First of all, let me correct that Dānlín and Li Zongwei play badminton, not table tennis. If you play badminton alone with others, then, it means one side, so it's called singles. Look, being single means being single.