My grandson obsesses about car keys with the keyless entry device attached. That is all he seems to care about. The other day I went to join he and his mother at the pool. He ran to me like he was excited to see me, only to ask for my keys. When I wouldn't give them to him, he couldn't even enjoy the pool anymore, he even saw a woman leaving the pool and asked her for her keys.
Before the thing with the keys (that's been going on for at least 2 or 3 months), he was obsessed with any kind of fan. As soon as he entered any room anywhere he immediately started looking for fans and continuously talked about fans. He also became obsessed with vacuum sweepers.
He is one of 7 grandchildren and I have never noticed any of the others doing this. He is a very sweet boy.
He doesn't sound obsessed. He is focused. His style of learning about objects is to focus upon them until he finds something new to learn about. He is probably very intelligent.
I would be a little more cautious about labeling children's behavior in such a negative light unless they have been diagnosed with a disorder and even then diagnosis are all about what is normal to the general population which means we leave little variety for children.
He is lucky you are concerned about him, however, relax and enjoy his learning style.
M Kay Keller