Sometimes using just a -po verb indicates existence rather than just place, but since there's a place after it ... I'm inclined to agree with you that this is not the best match.
To say "There are other students" I'd start the sentence with kuna or pana or, if I wanted to emphasise the "inside-ness" of their location, then mna.
I probably wrote "The other students are in the classroom" when I came across this sentence.
I was thinking the same, since it's inside the classroom. First they teach us how things that are inside something have to go with mna/wamo, and they teach us that we have to use pana for "there is" , and wapo for "something is somewhere", and here they happily breaks both of the rules
Well if there is any lesson to be learned here, it is that native speakers themselves can be very inconsistent in the use of these things: Question: Je, kuna watu huko? Answer: Hapana. Hamna mtu. I believe you could hear something like this, with "pa-, ku-, m-" all happily mixed together. I think the notes for the associated lesson make mention of this too.