Yes, I've also seen this quite a bit. I suspect this is because Duolingo has never been very good at presenting grammatical gender. Something that has remained a major flaw. The creators of this course have obviously attempted to do a good job at working around that, but as a result Duolingo is picking these up as real words when randomly picking words to present. That would be my guess, anyway.
This comment is more about Duolingo because in different languages they present sentences that do not make any sense. At least they should say that the cat drinks water, or the girl drinks tea. I don't know how this grammatically correct but out of touch with reality can be beneficial.
Hi Fjdv: My cat eats cheetos, there's probably one that would drink tea. Secondly, there have been plenty of times I've stared at a sentence here on Duolingo saying "That just doesn't make any sense!"... and then suddenly a way comes to me that I can make it make sense. And lastly, silly sentences are still teaching you real words and sentence structures.