First of all, it's a rant - categorized as such. It deserves a little slack for its use of direct language.
Second, I thought it was very clear that he was referring to writers who write rules-related material for D&D, not "any use of the word at all." If he came back and said that, it would be just silly. Rather, he is clearly (to me, at least) referring to calling something by a different game term from what it has been established.
For instance, a module designer writes up a new creature. He writes up that the creature has a sonic attack that "stuns" all characters who fail their save, causing them to be helpless for 1d6 rounds. "Stun" carries a specific connotation in the rules now, and it DEFNITELY does not mean "helpless." Would you let something like that slide in a module? What does the designer mean? Are they stunned? Are they helpless? You don't have to be stunned to be helpless, and vice versa.
Third, any time I write a reply that corrects someone's grammar, I check it FIVE TIMES AS MUCH as any other standard reply before hitting the "send" button. I do not mean disrespect to Shawn, but it makes you look like a goofball when correcting someone's grammar, yet you can't even get your own **** straight.
He makes some worthwhile points, particularly where game terminology is concerned. I somehow doubt Sean gives a darn where "In-character speech" is concerned. Sorcerers might well call themselves "Witches" for all they care, and sorcerer is the incorrect term.