Not really suspicion at this point. They are proveably 403 rejecting requests from the KBin useragent. You have the letters "kbinbot" anywhere in your useragent (case insensitive) you ain't getting content.
As a bonus they're still sending out stuff to instances though. But since KBin can't then resolve it it amounts to a DoS attack as the messages just build up in KBin retry queues.