"Senior developer" is a job title. Think of it as army ranks, each national army might have their own names and ways or promoting others.
Some people also argue what is the difference between calling yourself coder, programmer, software developer and software engineer, and even taking the debate as far as questioning if a software engineer is an actual engineer.
To be honest, these debates are sort of empty unless there is clear regulation and disambiguation around what seniority is. You can define seniority in many ways.
I think you've missed the point of the article. I thought it was going the "debate over words" direction you're responding to, but it ended up being a lot less about what the word means, and a lot more about what the concept of "seniority" in our field entails, which is a lot more interesting.
Some people also argue what is the difference between calling yourself coder, programmer, software developer and software engineer, and even taking the debate as far as questioning if a software engineer is an actual engineer.
To be honest, these debates are sort of empty unless there is clear regulation and disambiguation around what seniority is. You can define seniority in many ways.