Color that under "poor understanding of supply and demand."

Not really. I understand that Econ 101 gives a lot of people a mystical belief in the power of supply and demand. But real economies are not governed by one or two simple equations. If they were, building more and bigger freeways would solve traffic problems. It doesn't. [1]

As an example, look at how many Bay Area companies over the past decades have vigorously opened offices elsewhere, often moving whole slices of their companies to lower-cost areas. They are quite explicit this is due to rising costs. If costs didn't rise, or were rising more slowly, we would have even more demand for housing here. Or, put differently, reasonable increases in supply might not actually help current residents. But they could well increase pain for current residents: more traffic, more gentrification, more destruction of existing buildings and neighborhoods.

So it may be less "poor understanding of certain shallow econ dogmas" and "a strong understanding of what they stand to lose, and how often they've lost at the hands of affluent white people who are sure they know how to fix things". Consider James Baldwin, for example: https://www.youtube.com/watch?v=T8Abhj17kYU

[1] See, e.g.: https://www.wired.com/2014/06/wuwt-traffic-induced-demand/

Why? Why would a natural distrust of a group of people who has never seemed interested in their problems or wellbeing before be a "poor understanding of supply and demand"?

Your implication is that it is reasonable for this group to believe that NIMBYism will somehow prevent rents from rising, "because we don't trust tech workers," which is counterfactual. In this case, low- and high-pay renters' interests are almost entirely aligned.

My implication had nothing to do with NIMBYism. Just that they don't trust the tech workers to have their interests at heart.

Its entirely reasonable and possible to believe that neither group will promote an outcome that will help those people.