He is a big whale and he can manipulate the market but I do not see nothing ilegal in it, this market is not regulated (and I hope it will be always like this) so anyone can do what he want with their money.
That's not true. Bitcoin trading is regulated in many jurisdictions. For example, Bitfinex was fined by the CFTC a couple years back for the way they were handling custody for BTC margin trading. Similarly, no matter where an exchange is located, their jurisdiction regarding enforcement of securities laws and other regulations is based on where their customers live.
That's why, for example, Bitfinex restricted trading of tokens they deemed "securities" for US customers before pulling out of the US market entirely. Even though Bitcoin might not be regulated in the British Virgin Islands or Hong Kong (where Bitfinex is located), it is definitely regulated in places like the USA.