A fatwa is a legal ruling on a point of Islamic law (sharia) given by a qualified Islamic jurist (faqih) in response to a question posed by a private individual, judge or government.
So unless you live in a country that runs on Sharia law and have your real information connected to your account, you can safely ignore it.
You could report the poster for being mean if it goes against that community's or instance's rules. Up to you. But I think someone's just being a troll.
Anyone can call themselves an imam and give out a fatwah so long as they have people willing to listen. Its not like its an arrest warrant or smth, no legitimate party runs this.
i hadn't realized it was online tho. By reporting I thought op meant to the pigs.