Have him email me. We sometimes (depends on the team, hiring manager, etc) get things stuck in the process, even with good candidates. (Someone leaves a note saying "great interview, next he should talk to someone in one-of- the- teams, then it doesn't actually get assigned to someone, and just sits there.)

If we actually set it to "decline" we send out decline email, or something more personal.

I thankfully am not actually involved in hiring in any way. I don't really even interview many people.