I’ve never seen low-information voter used as a racist dog whistle, at least not when it was first used during the Obama years. Has it been used differently since?
UC Berkeley cognitive linguist George Lakoff, 2012: Dumb and dumber: The ‘low-information’ voter:

As the U.S. presidential campaign heats up, Mitt Romney and Barack Obama are piling up money and shoring up their political bases. But they’re also going after a few million voters in a handful of swing states — voters considered critical to winning the election. And within this bloc of voters is a special camp: “low-information voters,” or LIVs, a term that keeps popping up in magazines and political blogs.

The term is mainly used by liberals to refer to those who vote conservative against their interests and the best interests of the nation. It assumes they vote that way because they lack sufficient information about issues. The assumption being, of course, that if only they had the real facts, they would vote differently — for both their own best interests and those of the nation.

The problem is that, as neutral as the term “low-information voters” may sound, it’s pejorative and used to express frustration with these voters, who (we’re told) act against their own best interests. Liberals tend to attribute the problem in large part to conscious Republican efforts at misinformation — say, on Fox News or talk radio — and in part to faulty information gleaned from friends, family and random sources.