[cypher]

As April said having the ears laid flat is a sign of nervousness, it can also indicate health problems but that's probably not the case, just that he's new & a bit scared.
Make sure he feels safe in his cage/bin with some nice hideouts, a cardboard box with the base cut out will make a good temporary house if you don't have one yet & you can use things like bendy bridges to fill some of the space if it's too open.