It is that type of wiring and it's at least hooked up to a dial in the bedroom that controls the volume level of the ceiling speakers. Each of the colored wires are twisted with a white one
If that volume control is a normal analog volume control and not some kind of digital keypad getting signals over cat5e from some other device (possibly located in a single network location - mine happens to be in the master bathroom closet) then it needs 4 conductors from the source of the audio (the receiver).
It's possible that they used the single cat5e wire for that purpose instead of a more traditional 16/4 speaker wire. If that is the case, you are going to have to remove the wall plate and see how it is wired. They could have used 4 single conductors and left the others hanging, but I'd bet they kept them paired and each pair goes to an input on the volume control: left-, left+, right-, right+. From the outputs of the volume control to the speakers should be 2 sets of 2 conductor speaker wire. You'd be able to see the speaker wire if you remove the wall plate but that is not relevant to which of the conductors of the cat5e to connect to the receiver.
If my hunch is right, you just need to take note of which pair goes to which input on the volume control and then use that same pair at the receiver end. For example, if the brown and white/brown pair goes to the left- input on the VC, then use that pair for the left- on the receiver and likewise for each other pair.