He takes Chenqing and he starts by playing a few notes that aren't doing much of anything, he just wants to figure out how to play the flute, which he hasn't done since childhood. Once he's gotten a good feel of the notes he wants, he plays:

"We shouldn't leave physical written paper. Not unless we can ensure everyone will burn it."

Also it definitely took him awhile to parse what the heck an "Aziraphale" is. He figures it's one of the others, and by the context he's going to go with either the pink-haired girl or one of the two odd-looking men with large wings and familiar color scheme.

But now he has to think of the best way to explain how they know, without explaining Inquiry. How many people will think them mad if they say, "we asked the ghosts"?

He hands the flute back to Wei Ying.