No, your IP address cannot be seen by other players. Your computer communicates with the FlyOrDie server, not with the other player. But if somebody post a link here in the forum, you visit the link, then of course he (or more specifically, the owner of the target site) will see the addresses of all of its visitors. But he will not know exactly which FlyOrDie players visited it. 

He can identify your address if you send him an email or call him on Skype.

Even if somebody knows your IP address, that does not mean that he can hack your computer. (On the other hand, if for some reason he indeed can hack any electronic device in your home, than anybody can do the same, and you have a much bigger problem than a player from here).

In the anonymous world of the internet, there are many childish people who try to frighten others, with completely baseless stories.