So there was this Cessna Skymaster sitting at the bar and in walks this cute little BD-5. Neat looking little aircraft.
Czech aircraft with a number after a three letter rego code (OK-CUD-10) are microlights. Management of microlights is not a role of their civil aviation authority but the Czech light aircraft association. I haven't found a registration list for these guys yet but thought I would update the thread with this information for crowd solving the problem.