Well indeed, it's a single 250/300, but it could still have a split exhaust header, to breath into 2 expansion exhausts? Would be a great help in increasing the throughput of the header. With that pot I mean this thing:

- 2nd muffler on RH side.jpg (58.66 KiB) Viewed 1240 times
Which to me looks distinctly like a second muffler on the RH side, not a car bumper.
Btw, here's what seems to be the same bike, but now with a new header & that awkward LH expansion exhaust removed (which makes sense, as I guess it would burn your leg):
On it having a sidecar: see those square tyres, particularly the F one in your pic. Tyres like that will make normal riding difficult. Another indication is the handrail at the rear which, with a seat like that, can only be used by the monkey (= sidecarist). But I'm not sure as we haven’t' seen the RH side of the bike.