Say psych right now!
But maybe his injuries from earlier were more serious than expected and instead of running the risk of slowing them down or potentially getting them caught, he chose to sacrifice himself. Guy does have a bit of a hero of shadow justice vibe.
Or
That’s not actually him. For some reason, him coming strapped with bombs on his person without neither Uruma nor Kawana took notice beforehand. Basically he was switched out at some point. We have people who can make perfect facial replicas of Kaname after all