Or just sand it thoroughtly in the first place. I've never had the lettering reappear after painting. Is it really wise to smear glue all over an exterior surface like that? I've never heard of such a thing.
Never seen this either, but I think I "get" what he's saying.
When you injection-mold any part out of plastic, you get a "skin effect" where the material is much denser and more... well... "aligned" is a good way to put it... at the surface, compared to being more porous and more "randomized" internally. The depth of the "skin effect" depends on a number of issues, including injection pressure, injection temperature, mold cooling, the nature of the resin being used (filled versus pure, for example) and so forth.
If the "skin layer" is quite shallow, it's possible to see a bit of sinkage in the area where you removed material, potentially even leaving the nomenclature in a visible form. I've never seen it happen myself (the skin layer is typically thicker than the lettering, and that's by DESIGN, so if you sand away the lettering, you're still inside that very dense "skin effect" and you won't see what he's discussing.
If you did see that, it would be a very, very shallow "sinkage" where the lettering would occur, and a single primer-and-sand operation would totally mask any such effect.
What he's discussing is a way of "resealing" the porosity after sanding it away. Which, if this were present, would have the potential to give a smooth surface, at the expense of requiring multiple passes and probably removing a lot more of the plastic than you really want to lose.
In other words... I don't recommend this approach. Instead... sand it off, get a nice smooth finish on that area, then prime, and if you can see it, sand the primer layer (NOT the plastic) to eliminate this. Filling in with paint is preferable to trying to alter the internal properties of a molded plastic part, I think.