Hard to tell in looking at the head straight on, or what you have up there in the NW, but around here in MO, he looks a lot like the Bullsnakes we have. They are constrictors that feed on mice & such, and can be quite defensive [hissing, tail thumping, etc.} when frightened.
Around here, we only worry about rattlers, copperhards and cottonmouths. Compared to the non-venomous variety, they are easy to identify in that they all have a triangular-shaped head and "slit" pupils, like a cat. If I run across a snake without those characteristics, I leave him alone. In fact, to be honest, I leave the copperheads alone, as well, since they posess a very low key demeanor, rarely strike humans with venom, and do a great job on rodents and such. I'm a little more wary of the rattlers, and will kill cottonmouths on sight, since they can get somewhat aggressive in defense of what they consider their territory.
In any event, I think it's safe to say he's a "good neighbor," and you've aided yourself more in relocating him back outside than by simply dispatching him.
- Jay