"Tech debt" was coined as a metaphor to be used when talking to non-tech leaders, to explain why investment was needed into systems to keep them running, and not just focus on new shiny features to drive sales.

So the article is right - it isn't real. But also wrong in that the need for that metaphor is very real. If defining tech debt leads to uncertainly, I recommend skipping definitions and just focus on the purpose - to use the concept as a framework to help leadership and engineering find the right balance between new feature development and internal system improvements.