> FireBirdResultMetaData and found that the tablename is conveniently there already

I don't know much about JDBC, old and new, however, from the common sense:

Queries in SQL servers, Firebird too, may go directly (generate text,
send it to server for execution, get the result) or prepared (generate
text, pass it to server for parsing and precompiling, get the
metadata, fill in parameters if any, tell server to execute pre-pared
metadata)

In the shorter sequence there easily might be no metadata received on
the client at all