How is both putting cans by date in certain area of the home ocd and then also to have cat food everywhere be OCD also in one person?

Obsessive Compulsive Disorder is when people obsess over something, and feel compelled to act on that obsession. 

So a person is obsessed with making sure they remember to feed their cat, so because they are obsessed with that they leave cat food cans al around the house to remind them. 

This person is also obsessed with making sure they eat food in the order purchased so they don't accidentally let something expire and make them sick, so they organize their pantry in a specific way and freak out if it is ever organized a different way.  They freak out when it is organized differently because that does not ensure that they won't get sick from eating expired food.

Mental health is complicated and very complex.  OCD is not just wanting to wash your hands all the time.  It is being obsessed with a particular thought and then acting on that.