They do say that it’s the number of clappers, not claps that count, so yes, effectively only the first counts.

But then they also say that they take the value of claps from the clappers usual number — so if someone always claps once, that’s the same “value” as someone who always claps fifty times.

But they do not say what that clap value affects!

See https://help.medium.com/hc/en-us/articles/360036691193-Calculating-earnings-in-the-Partner-Program and then

https://help.medium.com/hc/en-us/articles/115011350967-About-claps