Earlier quoted context omitted.
It comes down to what brackets mean, and the reader understanding what is quoted. In your second example, the quote is clear, verbatim as quotes are intended to be. In the first example, what has been clear, precise syntax is not a matter of ambiguity. In your example, it's somewhat clear, but inference is required to understand what was said. The example given in the article actually does bring genuine ambiguity to…
Whenever I see “go home and bite [his] pillow”, I’ve always assumed the person spoke quickly and/or skipped a word, which the editor thought should be added. It never occurred to me before now that the editor actually replaced a word!
Replacing a word breaks the syntax and brings ambiguity to some use cases involving brackets and quotes that did not have it before.
As I mentioned elsewhere, a similar thing happened with the one space vs. two spaces to end a sentence.
In that last sentence, there is now ambiguity after "vs. " where there was not before. Right now I am on desktop, but if I were to input that sentence on my Android, "two" would be auto-capitalized, even though I am mid sentence.
I see this headed a similar direction.
Cases where the actual verbatim expression may be made more clear with something added in brackets will now overlap with cases where someone wants to replace a word in a quote...
Sigh :(