Fox is looking for nearly any reason this happened that's not the one the killer literally wrote a 100+ page manifesto about: The Great Replacement. They've spent years giving this worldview hundreds of hours of airtime to the point that it's one of the main talking points on their most popular show in Tucker Carlson Tonight.
Making this issue about guns ownership and video games is convenient for the network and, as they have no shame and their viewship are not the type to think critically about this kind of thing, there is zero downside for them.
I think it's the same with any news network like Fox. They say things that they know that will get them views it's why the entire time trump was in office CNN never said a single good thing about him and why Fox had nothing but good things to say.