That's easy, to make sure you were paying enough attention, what with "ulo" and "ujo" being easy to confuse at a glance, this is less a nonsensical sentence, more the Duolingo equivalent of those tests you'd get in school that had a long list of instructions that started with "read everything first" and ended in "Don't do anything we just said other than put your name on this paper"
Looking at this sentence, I would never choose "jail cell" as a meaning for "ujo". I would think more along the lines of locking up court records or locking up evidence.
However, that's because where I'm from, there is a clear seperation of duties. A judge can sentence people to jail (or to prison). The sheriff is the one who lock people into cells. (Well, actually, the sheriff's deputies; the local sheriff's department has a staff of over 600 people so I doubt the sheriff does any of the grunt work.)
I'm sure that there are places where this isn't true. In particular, small communities may only have one person who handles everything from arrest to sentencing to jailing.