In other words, you can't use IMAX to generically mean large-format movie. This is because once you let that happen, it becomes incfreasingly difficult to protect the trademark, and that is where the confusion comes in.
That's not correct. You absolutely can use it generically to mean a large-format movie, just the same as many folks use "Band-Aid" to mean an adhesive bandage and "Kleenex" to mean a tissue. There's nothing in trademark law stopping you, as a regular person, from using protected marks in your everyday speech in whatever manner you desire. You can disparage them, you can conflate them with a knock-off, or you can even use the names incorrectly. Trademark law doesn't cover any of that.
What trademark law does (and what your own quote even says, though you seem to have missed it) is prevent the use of protected marks in commerce. You cannot make a large-format movie product and brand it with "IMAX", any more than you can make a tissue product and call it "Kleenex" or make an adhesive bandage and call it "Band-Aid", because doing so would cause customer confusion regarding which product is the legitimate one and which ones are knock-offs.
A news article providing a quote from a person that makes mention of a protected mark does not mean that the mark is being used in commerce. The article is simply quoting someone who mentioned the mark. Were the site called "IMAX's Ars Technica", IMAX would have a valid claim against Ars, but merely using the term, even incorrectly, in a quotation from someone else is in no way engaging in commerce, and as such does not fall under the quotation you provided.