Some of these comments are way too harsh!
I agree there is nothing wrong with your behavior. I think people are insensitive or just ignorant of others financial situation.
There are a lot of people who can't afford too many unnecessary expenses. Still there are those who never had to think to much about expenses like drinks in a bar or food in a restaurant. They might not even be conscious of the fact that the people around them might have it different.
Then there is the general stigma around money, especially not having any. Many people are actively afraid that others could think they don't have money. Feelings of shame and embarrassment around money are not uncommon. These are strong enough to lead to second hand embarrassment, seeing someone else showing signs of not having money. This can be very uncomfortable for them to experience, especially if they weren't aware of it or don't have much experience with it.
That is why it's nice not to assume that everybody in the group can afford to go to a bar. I know it's not easy to talk about money, but I think it's important to be upfront with your wealthier friends if you can't afford to go to the bar. They might reconsider going to somewhere else or someone's flat instead or just invite you. It shouldn't be upon the less wealthy to do this, but it's an unfortunate reality in most circles I know. The only exceptions are circles where it's common to have no money...
As for the bar and staff: they might talk and joke about it, because it's unusual, but they would be pretty short sighted to mind it. If you come with a group that pays, they make money. You could always leave and find some place that doesn't mind that one of you won't order anything.
You could try a sort of compromise and order a glass of tap water, assuming that it's free in your country of course. That way you order something, but make it clear that you won't spend any money. You are not sneaking in and instead being upfront with the staff.
In any case don't let yourself get bullied into spending money, when you can't or don't want to. I have myself been in the situation often enough that I couldn't really afford such expenses or rather wanted to save my limited money to spend it somewhere else. It's already an uncomfortable place, made harder by situations like that. However, there is nothing wrong with not having a lot of money and being open about it.
Here in Germany it depends on the region. But even within one region it can be different from friend group to friend group.
I grew up in southern Germany with handshake as default greeting. Except women often get a hug instead. If you know someone well it's more likely to greet with a hug with men grasping each other's hand before a short hug and slap on the back. However, if you see them a lot you might just give them a nod. On the others hand id you haven't seen them in a while they get a hug.
In East Germany, where I live now, it seems to be much more common to hug your friends. Interestingly some will put their head on the right, reaching with their left hand over your shoulder. Which can be very awkward, when you are used to the opposite and almost kiss.