My grandson is 2.

[JeanOG]

He has no speech problems, can communicate and is sociable.   He likes to focus on a specific task repeatedly (lining up his trains), twirls around looking up, has screaming fits, throws himself back with no concept that he might hurt himself; I am not sure if it is a behavioural issue or if he might be within the spectrum.

[Sandman2]

My opinion is that as long as he is social and can communicate, he is probably fine.  My grandkids are two and three.   When they find something that they like to do, they will fixate on that so I don't think that lining up trains is unusual at all.   And twirling around while looking up is actually a pretty smart thing to do as you are looking at a fixed place.   So I think he is fine.  enjoy him and get involved in whatever he is doing.