Outside can definitely be overstimulating. He might not have even recognized you when you went to pick him up. He might have been on sensory overload.
Maybe in the the future, either keep holding him, or if you put him down, use the hook (if he's tap/hook trained) to let him know it's you and he's going to be picked up.
Yes, I think he was definitely overstimulated by all the sounds and smells. I left him roam for quite awhile before trying to pick him up. After seeing his response, I immediately when inside to grab the hook which worked like a charm. Lessons learned for next outing!