"What do the strange words mean?"
Translation:Co znamenají ta zvláštní slova?
Not in standard Czech.
"znamenajou" is a dialectal form in some parts of Moravia, along with "znamenajú" and "znamenajó" in other parts of Moravia, or "znamenaj" in many parts of Bohemia (incl. Prague). So as you can see, the 3rd person plural has a variety of endings depending on the region. But the only standard form here is "znamenají".
It seems to be that, if the answer you give is too far away from the answer that DL expects, it will present an alternative "correct" option based on the answer you gave. Sometimes those alternatives seem totally weird, because they include words or constructions that we haven't yet learned. But they do give us some exposure to what we may be learning in future lessons... even if they confuse us now!