He was ill. He should have stayed home, but he couldn’t afford to.
Also, he took a perverse joy in touching as many surfaces as possible in the office. He made sure to touch the door handles especially, since everyone touched them and nobody sterilized after.
The elevator buttons were another good target. Everyone pushed those at some point.
He didn’t bother with the buttons going to other floors. He had nothing against the other companies in the building.
When he closed the door to his room at the end of the day, he fell into bed, tired but happy.