I too was confused why they tried to tie the two events together. The lead pipes had formed a coating (and this is true in other locations too) that made them nontoxic but when they were flushed with acidic water (as the water treatment plant did) they shed that lining and it began washing through the lead and putting it into the lines. The lines had operated fine with water from a different location that had different pH levels, but pH variation is common without pollution, so blaming this on pollution is a bit nonsensical.
When it comes to the article, it makes sense that pollution would be in poorer areas. Pollution lowers property value, which allows poorer individuals to live there. Or the area could have already been poor and they are unable to afford to leave.
I'm not sure who is to blame for the Flint crisis tbh, there seems to be a lot of finger pointing and politicizing. I have yet to find a source that wasn't biased one way or the other, which is sad. People just want answers and for it to be fixed.