> In philosophy, a razor is a principle or rule of thumb that allows one to eliminate ("shave off") unlikely explanations for a phenomenon, or avoid unnecessary actions.
I'd say maybe the rule here allows one to eliminate the useless parts of an explanation, thus simplifying the process of coming up with explanations for complicated things.
A razor is when you have a large number of potential explanations and want a simple rule to check if it worth further scrutiny. Occam's razor is the most famous, it says that the simplest explanation is probably the right one, Hanlon's razor is another one, it says that stupidity is more likely than malice.
Here it is just a guideline "don't dumb down", but there is no simple rule that tells if a message is dumb or not. For example, in the topic of science, a razor could be "numbers without error bars are dumb". It only takes a few seconds to see or not to see error bars, so you can quickly drop the ones without to focus on those that have.