Think the artist forgot to finish the manuscript before they hit "send to editor".

That reasoning falls apart pretty easily by one fact you admitted upfront: Alternate Japan. If the reader's to assume a modern Japanese setting, there'd be authorities investigating the orc killing on what is a low-level floor instead of chalking it up to the bad luck of adventurers. Something so serious would not merely be written off, especially as there were witnesses to the sequence of events. Instead, it's more reasonable to assume the standard isekai flaw is in play: focus hard on the MC and the gimmicks and ignore the actual establishment of the setting.