It was an incredibly easy question (yes this if ofc relative blah blah blah) because of how easy the eliminations were.
You already touched on why algae and fungi were easy eliminations. Proto- is imo a well known Greek word. Even if you don't exactly know what it means you've definitely heard words like prototype or protocol and can deduce that that they nothing to do with wandering.
So the most difficult part of the question is deciphering what is more likely to mean wandering. ZOA or plankton, which, if you know what a plankton is, seems like the most logical guess.
So you crying wolf is pretty hilarious given how simple it was to POE the answer with what I assume most people would consider basic knowledge.
Also, phyto means plant so I'm not sure at all sure why you think your argument holds any water