Diggle can say all he wants. He can yell, scream, throw another temper tantrum, but there's not much he can do when he's strung up like that. Hopefully, Oliver and the rest of the team will come to his rescue.
Felicity: What's going on? Ray? Ray: Oliver Queen is the Arrow. Felicity: What? Ray: I have a 140 IQ and three PhDs, but it's pretty hard to insult my intelligence, but I'm pretty sure you just did. It all makes sense now. Your, ah, sudden disappearances, your apprehension of helping me with my mission. You've been working with the Arrow this whole time.