It is a Muslim and African thing. As for why? I am afraid I can't really answer that question it could do with culture it could do with just what is at hand for a weapon. I will admit to not understanding the mindset behind that attack besides that it is designed to be as painful and scarring as possible.
It has become more popular in recent years in the west while yes correlation doe not mean causation. There are trends I would argue exist.
I am not saying that acid attacks aren't a feature of certain cultures outside of the UK. What I am suggesting is that there seems to be more than a few attacks in the UK not committed by Muslims, instead by whites. In the UK, it doesn't seem to be an exclusively Muslim/African phenomenon. That link that you posted did nothing to speak against that.
Pretty much. It's inherently a premeditated crime and should be treated as an absolutely heinous act with very harsh penalties. No one walks around with fucking corrosive acid for self-defense, except mad scientists, loony alchemists and bored crazed mages, neither of which exist in any sort of tangible capacity.