That's very much the point. The FBI can make an argument that they weren't trying to gain access (since a real attempt to gain access would have looked differen

That's very much the point. The FBI can make an argument that they weren't trying to gain access (since a real attempt to gain access would have looked different from "entering miscellaneous strings"). They were trying to see what the system did when authorization attempts failed. As far as I know, there's no law against that. It's similar to going through a suspect's trash.