I am not singling out based on whether I agree with it. I've been very clear. I don't ascribe to the silly notion being bandied about in this thread that 'BLM' is political messaging in the same sense of presidential campaign slogans just because politics is incidentally involved. By that standard, 'Together, anything is possible' is a political message. I don't equivocate so brutally that slogans such as 'Yes we can' or 'Make America great again'--slogans directly linked to promoting candidates for office--are the same as any message someone can somehow lump into being part of political conversations of the day.
This isn't comparing ads to ads.
Political issues are still political even if they aren't for a candidate or party.
That doesn't have to be relevant. Suppose hypothetical town Restrictedville with Republican Mayor Adolf Smith enacts a law that public area A is for candidate signs and public area B is for issue advocacy. In a sense, Restrictedville may not be
content-type neutral depending on some other factors, but they remain
content neutral. For example, each political candidate and each fan of political candidates has the same exact opportunities within public space, completely independent on whether they are promoting Trump, promoting Biden, Vermin Supreme or whoever AND each issue advocacy group and its proponents also have the same opportunities as each other. It's only when you cross content types that there may not be the same level of opportunity but this is because different content TYPES are different structurally. For example, every year there is a voting season that goes crazy with signs and the signs become a distraction to drivers etc. So, the town may have decided to restrict this content
type to specific areas of driving where drivers are less accident-prone while driving. Meanwhile, issue advocacy may be so rare a thing to make murals on public spaces that the town may allow permits to do so for a specific amount of time so that streets are not full of murals year long, frequency determined empirically...
Now whether or not I personally agree with such restrictions is irrelevant, the question is whether they are discriminatory (or not neutral to content), which in this hypothetical situation, they are content neutral.
But honestly, this is only an abstract concern. The city officials said they removed the mural because of complaints about traffic risk. One can see that conservatives have been complaining about traffic risks, too. We ought not assume just because a single person asks for a MAGA mural and the city erased the BLM mural that the one was because of the other. There is another plausible alternative.