yes, if he puffed out like that, bearded all big, and opened his mouth, clearly he saw something he didn't like. Joga did this about the 3rd time I took her outside, puffed out, bearded, open mouth, froze in her spot. I spoke softly and stroked her chin until she settled down. We go out a couple times a week and she seems to really enjoy it except for the occasional bird that flies a little too close, she'll puff out momentarily and then go back to doing what she was doing (which is mostly sitting there and looking around).
So I wouldn't stop taking him out, but you should absolutely put a harness on him...so many stories of beardies on this board going 'wild' when they get outside, they can move really, really fast...disappearing in the backyard for weeks on end - in most cases the endings are happy with the beardie miraculously reappearing...
This is the harness Joga has - it was made by Christine (oglepets) on the board, you can search her and see if she's still making them...they are comfy and are made well to keep the beardie from wiggling out of them: