Is it just the picture.. But the wheel with the 285 tyre appears to have a much more "inset" shape to the 5 spokes.. Which says to me that's one of the wider back wheels.
Is it possible someone messed up a tyre change and you've got a narrower rim with a wide tyre on the back!?
Only way to know for sure is pull off the wheels and read the "J" size from the stamps on the back of the wheel.
Could just be an illusion, but the first picture looks much "flatter" to me.
My mistake. I thought you had taken pictures of the two mis-matched front tyres

But its just a front rear picture

O:-)
I assume the previous owner didn't try rotating the tyres and leave you with a wider rim on the front, and then change a back tyre without thinking about it... Check that you have the wider rims at the back with the correct tyres, and then have your fronts sorted
