The proportions look more like RJ11 than RJ45 to me. Not how big the clip is compared to the plug. Of course this is a hand drawn icon so take everything with a grain of salt.

Are you sure it’s not meant to be an RJ45 plug? The cylindrical thing to the bottom left corner of the wall socket looks like it might be a BNC plug. Which would make sense for the era of quake when Ethernet wasn’t yet ubiquitous.