If Manoah had understood the identity of the visitor, honouring him would in itself be fine, given his divine status. But Manoah has yet to perceive whom he is talking to, and as such it would be misdirected honour, as only the Lord is to be honoured for opening a barren womb. A further problem is when Manoah wants to honour him that is the problem: he wants to honour him not right away but only when your words come true.
That says that Manoah is still doubtful about the words of the Lord.1
17 And Manoah said to the angel of the LORD, “What is your name, so that, when your words come true, we may honor you?”