Aziraphale looks over in the direction Ian points and immediately relaxes when he sees who it is. Harley comes with her own particular brand of teasing, but so far as Aziraphale knows, she's unaware of the pie reference. Truly just a reference to the number, then.

With a much warmer expression, he smiles at Ian. "Good thing you have that particular song memorized. A useful number, that, or so I'm told." He offers a hand. "My name's Aziraphale. Was that the extent of your dare?"