i think it matters because the amount of bitcoin held by him.
Discussion
How does it matter. BTC doesn't get more valuable in fiat terms because 700 thousand hasn't moved. It gets more valuable because fiat is broken and there are only 21 mil BTC.
it matters if he sells for fiat.
Well I don't think so because everyone knows there can only be 21mil, so the worst that would happen is that the price would fall for a limited time until the supply vs demand comes back to equilibrium and then we can all continue buying the top forever.
what if he coordinated an attack by buy majority of the hash power and forked? is that possible?
Honestly I don't know for sure if it is possible but I think there are a couple reasons it wouldn't work.
1- he would destroy the value in the BTC he holds
2- trying to corner a market like that is always a moving target. As you buy gold, silver or hash power or whatever the price increases at a rate that you can't keep up with.
This is of course assuming he was a bad actor but I don't think he is otherwise he wouldn't have invented it in the first place.