The author isn't wrong that "Senior" is probably a bit of an inflation for what it means in the industry - competent enough to work on medium to large projects with little oversight - but Staff, Senior Staff and Principal titles all exist to fill the gap the author is talking about, as does architect, although I don't see that one as often. It's definitely confusing if you aren't intimately familiar with the industry though.
For what it's worth, I can't think of any notable company where senior is anywhere close to the terminal level for a software engineer.