I believe these two statements are accurate, though I'm happy to be corrected if they aren't. It's been a few years since I wrote C++. Beyond that, I see my claims as "abstract" and not "falsehoods".
I don't know when you went to school, but most places still teach using C++98, which is two generations removed from current practice. It is not unusual for TAs assigned to teach C++ to resent being taken away from their glorious combinators, and teach their resentment.
If coding C++ was not immense fun, you may be certain you were Doing It Wrong.
The author isn't claiming to go into a deep dive into C or C++. They are trying to talk about Rust. Your argument seems to be against the author's use of "C/C++" vs. "C and/or C++", which seems to me like some nitpicking, as the author uses "C/C++/Rust" later on. It isn't like they are pooling the languages as being the "same". Rather, they are talking about having similar, lower-level of control over "strings" as a data structure, as opposed to the primitives they seem to be in other high-level languages like C#, Python, Java, Go, Kotlin, Swift, or JavaScript.
And yes even if you give them C++20, many devs will code in the C subset, because a large majority doesn't care, isn't in HN or Reddit, or even bothers to spend hours of their life watching CppCon, C++Now or ACCU talks, unless it is mandated by their boss.
I imagine you know who Lakos and Victorio are on the C++ community,
"C++11/14 at Scale - What Have We Learned?"
This "C/C++" bad habit is very commonly used, around Rust, to slyly imply there is no effective difference, but in a way that permits an injured response to criticism that "it just means C or C++". But it doesn't, unless you are talking about object file symbols or compiler optimizers; and often enough not then. What it does is encourage sloppy thinking, and resultant falsehoods. These falsehoods show up in the article, revealed if you change "C/C++" to "C or C++" in each case.
In several places, it says just "C++" yet is clearly still talking about C. It is OK not to know C++, or not like it. But things are hard enough without active falsehoods. It is not hard to get it right: if you are talking about C, write "C". That will always be correct. If you are talking about C++, say "C++".
Rust stands or falls on its own. It doesn't need invidious editorializing.