My son did the same thing!!! He would line up his ride on firetruck, lawn mower and dump truck at my one closet door. One day I needed to get in there to get something out so I just opened the door and it pushed the toys away. I closed the door and left the toys now sitting at an angle. He came down the hall and freaked out when he say them!!! He lined them back up and walked away. He would do it with hotwheels too at night. Line them up on my leg while I sat on the couch, when he'd go back to his room for more I'd move them or we'd put them on daddy's leg. He would take them back, put the back at my leg and go about his business!
But he just has this way of things needing to be just so. If he is holding a hand rail while walking, he has to finish it if it curves around, walking the curb-finish it. Stuff like that. He's 4 now too and the toys aren't so much an issue but he still does it. Is it OCD like?? Maybe. He could also at age 2, point out a hotwheel car at a strangers house or in the isle at the store that he already had. And would point at the front end of a SUV and say it was just like mine and it was the same make/model as mine! Does it with the other 2 trucks we have too. Maybe we have smart kids on our hands :)
We joke about it too especially since he has a great Aunt that has some OCD issues. And a friend of ours has OCD with numbers, counting and organizing and he even said it could be OCD but too young to tell. I try not to make it an issue just in case it is.
So yeah, I'd say your son is normal. At least to me :)
S.