But there's a difference between a bang bang offside call and a missed foul call no?

Managers, including Arsene, always bitch about the latter. But the former, you don't see a ton of bitching about, because that tends to even out.

...as they often and, in this case, lead directly to goals. A foul call outside of the area leads to a goal what? 5% of the time? 10%?

The foul call can be just as controversial and bang/bang as an offsides call. I would think that most managers would bitch about either circumstance, but I rarely pay attention to managers' postgame comments, even Wenger's.

Edit: There was also a similar bang/bang offsides call against Arsenal in the 1st half. So part of the problem was that it didn't even out.