Receiving gift from student before grading MSc thesis. Is it ethical?
In my opinion you are asking yourself the wrong question. The important problem is not if it feels like a bribe to you, but if it could look like a bribe to others. 

Let's say you have another student whose thesis you are grading at the same time and he ends up with a worse grade. This might have been an objective decision, but still, if this other student now hears about the gift you got, he will start to wonder if maybe giving you a nice gift would have gotten him the same grade.

Since the gift is quite small, you are most likely legally in the clear, however in my opinion, ethically it wasn't the right thing to do. It is probably to late to return the gift right now, but for similar future situations, it is probably better to decline gifts until the grade is set in stone. Not only from an ethical point of view but also since it will give you an aura of fairness and incorruptibility at the low cost of a few cheap beers.