I wouldnt worry about it, so long as hes curious when hes on lead and not shying away it will mean that he wont at least be getting into scrapes at distance.
My 8 mth year old is the same.. hes had my older dog for company since 8 weeks and has been in training lessons since 12wks with a variety of other dogs, in lessons hes keen to sniff around them unless otherwise told but out and about its very rare he will instgate play - hes more intent on disturbing the undergrowth