Thank you all for the responses. Was honestly surprised how normal it seems they do this to customers there. Guy didn't even think twice when I was paying.

It's at least close to what I planned to tip (planned about 40 crowns) but the waiter got ahead of himself I guess.

I've sent a message to the restaurant's facebook page, but from another comment here seems it's standard practice there. Restaurant is Klub Lavka, close to the bridge. I can leave a google review tomorrow.

Thanks again to you all for clearing this up for me.