He is probably from a 3rd world country where that amount is a big deal. He seems desperate which is why he is trying everything to try and reclaim his funds which sadly won't help since 1xbit rarely returns gambler funds.
You have 1000 Billion dollars. So what do you not need your fund which is on your right? No one can give up those 400$ dollars without any valid reason. The person has become scammed 400$ dollar which can't be considered spam, revenge, or something like that. Hence it is the right of that person to claim that 400$ and also it is his right to let people know about the scam.