There is a big difference between
modern C++ (C++11 ff.) and even the most current iteration of C. The two languages might have been quite similar back in the day when "C with classes" was created, but they have diverged significantly since then. Therefore, I think it is wrong to consider C a "proper subset" of C++, as often is claimed, or even to treat them as equals.
In other words, the real fallacy of the original post is throwing C and C++ into one pot, as if it were all the same - something I consider could not be further from the truth, even back in the C++98 days. A part of that problem is that persons having a (possibly incomplete) understanding of only one of the two languages (on top) believe they can apply that understanding to the other language, too, without having to learn the correct idiomatic usage of the other [1]. And that situation is made even worse by posts that claim to only have to point out some "gotchas" you need to be aware of to understand the other language, particularly coding in C after picking up some C++. Just to name the most critical changes in C++ over C: RAII, abstractions (objects/polymorphism/templates/generics), I/O, error handling, and namespaces/encapsulation. However, not even keywords work the same (fe., `const` and `typedef`). Finally, when C code breaks, it typically is closely related to one of those features that would have tooling in C++ to avoid the issue (in particular, containers to avoid resource leakages in connection with more advanced error and I/O handling techniques).
In other words, I pretty much agree with the GP about the hyperbole of the linked blog entry, and would only let the original post "stand" if it had some kind of significant `C != C++` distinction. I can agree with anyone who thinks that coding in C is probably a Bad Idea today unless you must due to maintaining legacy code-bases, while I think that C++11 has greatly changed the issues you have to look after when coding in C++, making it a lot more safer - and IMO quite fun - to use.
[1] https://olvemaudal.com/2011/10/10/deep-c/
(note that all C++ issues in the post can be avoided by using proper modern C++, like "naked" `new` usages and such)
[minors edits after the post for spelling corrections and readability - but no semantic changes]