What if it were saying, "you all come now?" There should be two correct answers in Swahili.
Many English sentences that require "you" to be translated into Swahili have this problem. Most only the plural is currently accepted but there are some that only accept the singular. It's a pain.
At this stage I think it is going to take a long time to see the necessary corrections and additions made to the course. Too many reports, and the team are active Peace Corps members. Plus, being in beta they don't have as much control over the editing process.