Sorry mate, I couldn’t resist.
My experience is that the informal meet & greet is quite common. I know in my field(sales, marketing, retail) that this is very much a first step in the process. I’ve done it on many occasions particularly to see what a candidate is like in just a casual setting without the fear of the whole ‘what are your strengths/weaknesses, best achievements, blah, blah’ line of questioning that you get a formal interview. I know I would prefer to test the working relationship potential in that sort of setting(also, you see the candidates interaction with staff in a coffee shop for example).
Also, it might also reflect the company in that they are quite small & do things without the layers of BS you’d get with a larger company.
Not sure if this is of use to you but hopefully just adds to the picture you’re trying to form.
Irrespective, good luck & if its a job you want I hope it all works out.