it's totally fine :) don't worry. if he gets older and is anxious to be around others, then maybe you can worry. but even then, some kids just like to be alone... im like that. i have times i like to be alone, but im actually very social.
Sounds normal to me. I spent the day with my nephew yesterday and he was just like that. Totally content to just sit on the floor and chew on the toy he was playing with.
Enjoy it while you can. I'm sure a clingy stage will start before you know it!