It was Germany’s submission for foreign language/international, and voters apparently liked it enough to vote for it in both categories. I think it does make sense to vote for it in both, if you include it on your preferential ballot for best picture but aren’t sure it will get that nomination.
“Anatomy of a Fall”, on the other hand, wasn’t even submitted by France.
All that aside, this is the first year that two foreign language films have been nominated for best picture.