What does it mean when a guy brushes up against you?

this was In a semi empty hallway when it wasn’t necessary for him to do so. You could tell he did it on purpose & it wasn’t just a light shoulder brush it was his whole body brushing up against my side. 
We are not close friends just acquaintances we talk once in awhile. I was walking in front of him & he caught up to me just to brush up against me & kept walking forward without saying anything.
he’s greeted me on 2 other occasions. 
The first time he was walking with his friend and simply waved at me then another he said “sup (my name)” 
If he’s just being nice why was it necessary to brush up against me