S.H.
That's what 2 year olds do. From about that age... their cognition develops more... and they get "orderly" and like to categorize things... it shows and it is because... they now can generalize about shapes/sizes/types of object and color... and then group them together.
It is a learning process.
It is normal.
It is cognitive development...
He probably does that at Daycare... because of all the chaos there and so many kids... and all the stimulation/activity that goes on... and doing that is more relaxing for him... and he is teaching himself things.
Kids learn... by repetition....
He is NOT... OCD.
Both my kids did things like that too.
Still do.... and they are 4 & 8 years old.
all the best,
Susan