No it's to support the weight of the seats. Having the bar there means it only has to be supported from one side and isn't blocking floor space by the aisle. The wire for USB and power is a lot smaller.
It does look rather substantial just to carry some wiring.
On another matter, it's interesting how low key today's "launch" was.
By comparison when Greater Anglia ran their first FLIRT they had had an advertising campaign beforehand (including a rather impressive sand sculpture of a FLIRT in (I think it was) Great Yarmouth station). Then on day one they had free hot drinks on the train and handed out merchandise. Now that might not work for the rush hour, but it could have been done later in the day.
I just looked on Wales Online and the most recent story I can find about TfW is about how disruptive the Metro works are (with someone complaining - understandably - about the extra time it takes to change onto a bus for part of her journey,
but then saying that even when there are no engineering works the service is poor and something should be done to improve it....)