I think it's a bit unusual. Most puppies want to be with their owners ALL the time.
However, (I don't know where you live), he might just enjoy the cooler weather???
Kyleigh LOVES to just sit on the deck when it's cooler outside. I make a point of being "around" the back door - kitchen / living room area of the upstairs when she wants to just "hang out" so I can hear / see her.
At 6 months I certainly wouldn't want to leave him alone too long ... too much time left to his own devices might not be a good thing (i.e. digging, chewing, etc.) and I don't know what kind of neighbourhood you live in (is it safe to leave him outside unattended?)
Marionís Zoo-Kyleigh, Raylan-cat, Echo-TAG,