Buses can be repainted.

But if the list was longer, what is the explanation for why, out of all the possibilities, they chose the NHS? Was it at random? Or did they have a reason to select it and if so, what was it?

I suggest it was not accidental.

I also suggest it was to make people think the funds would be going into the NHS. To deliberately compose a slogan that appears to say one thing nut on careful reading says another is something to be ashamed of, not proud.