OKAY I've been thinking and writing Jack's history and such and I have two options for ya, lemme know which one sounds better.

One is that Jack is making technology to help locate other supernaturals, which may come in handy as being an outreach person, so they could interact that way and it could just be tenuous and we can run into fae trouble later OR

Another would be that they ran into each other while it was obvious Aziraphale was fae, and though he got away from the Hillingdon when Jack scars up his face, maybe he blackmailed Aziraphale to cast longer lasting illusions in order to hide the scar?