A by no means unknown situation, and nothing to do with what is described above, but more prevalent on carriers with short turnrounds and/or crews scheduled to the hilt. Were the bags deliberately left off to save time getting ready for departure from Budapest. This is commonly concealed by blaming it on incompetence by the baggage loaders, where in practice it is a carrier decision to depart before the bags (or some of them) are loaded. Pax are never told.
Hopefully at least a scribbled update to the loadsheet. Complain to the Irish CAA and ask them to pull the Ryanair loadsheet for the flight in question.