Answers derived from the actual ruling. (Translate yourself if you don't believe me. :P)
Is a web site visitor a customer?
If they used some Google service, then yes.
Or does some form of payment for services need to be made?
No.
What about android users, does having an android device make someone a customer or would google need to sell the OS for that to count?
If it's only about the OS, I think the seller would be the only one the user has a business relationship with. But since almost any Android device includes Google services - yes, I think practically every Android user is a customer of Google in the legal sense.
It sounds like the Judge ruled that any person who uses a google service is a customer even if that service is free.
Yes.
It seems like that is a win for the consumer, but I have to wonder if that was the correct decision in this case. It doesn't seem unreasonable to me to need to be a paying customer for a company to expend resources to adequately respond to your communications. Some questions can cause hours of follow up work to send a reply.
If Google decides to discontinue all Google services in Germany as a result, would that really be a "win" for the German consumer?
You are of course free to argue about the merit of the law. But the ruling is "correct" in the legal sense.
Personally, I think Google is making a shitload of money in Germany and they should be able to use some of that to talk to their customers. They would be unbelievably stupid to shut down operations here just to save the cost of paying a few people to actually respond to email.