I can't say I know for sure, but I doubt Bulgaria made this fuze. Unless the person you're talking to can offer evidence or a credible resource, I would assume it is a Czech-made fuze. I have two of these, and they look exactly like the one in the picture you linked, and they also have no markings. But if the fuze you're looking at looks different in some way, even just the color, then maybe it was made somewhere else. If it looks the same, it's Czech in my opinion.
I doubt Bulgaria made this fuze for three reasons: 1) It is not a very good fuze and is prone to catastrophic failure. 2) I have seen no evidence in any reference materials of anyone but Czechoslovakia using this fuze or the mines it works with. 3) When Bulgaria copies other countries' ordnance, it seems like it's always Russian stuff, and this fuze is incompatible with Russian mines.
I doubt anyone copied the RO-2 because it's a piece of crap. Czechoslovakia has made some great things over the years, but this little bastard is a Ford Pinto.
The RO-2 fuze works in AT mines where the pressure plate is designed to 'tip' to the side and break off the top of the fuze, releasing the striker. The Bulgarian AT mines I've seen are based on Russian designs with much more complex fuzes (either clockwork, pneumatic, or electronic) and which require downward pressure on the fuze.
These are my ideas. I hope they help.
Rob