You can access substantially all internet services from France, and from any other country that doesn't explicitly block them, and from most of the ones that do via satellite internet or VPNs etc.
> you can create an account from a French number.
You can have a French number and not be in France. Also, this is the location of the user, not the company. This is basically the same reasoning as the internet; the phone network is global and anybody can call anybody. That doesn't mean that every service provider is in every country.
> Also the website is in French and the illegal messages are likely in French.
There are millions of people who speak French who aren't in France.
> Now add on top, that the CEO is French on French soil...
But we're talking about where the company is operating. Should France arrest the French CEO of a US company that does something in the US which is legal in the US but not in France?