Take "until," which the author said was ambiguous. I absoutely agree and have thought about this not just when writing fiction but when doing work (legal writing). If you have until April 15 to file your tax returns, does it mean you have to file it no later than the end of the day on April 14 or do you have until the end of the day on April 15? As you all know I am sure, we are all happy that the tax authorities are more specific and specify that the due date is April 15. Certainly an easy hang-up or pitfall to avoid in your writing.
"Next" also made the author's list of ambiguous words. It is Monday morning and you are making plans with your friends for lunch next Thursday. Does next Thursday mean this upcoming Thursday or Thursday of next week? Again, this is an easy pitfall to avoid.
And then the article got interesting... discussing the use of the word "American" to refer to persons who are US citizens or other persons who are considered "US persons." The author opined that using the term American to refer to US persons is fine (although technically incorrect) because there is no other single word we can use to refer to a US citizen and because most people in the US and Europe will assume that an American is a US person, as opposed to a Brazilian or Mexican person. Maybe this usage is commonplace and, as such, is becoming acceptable, but you should see the responses given to the article by Americans who are not US citizens...
Writing, like everything else, cannot escape politics.