It is true that they are different, but also, given the significant overlap between the two, people will reasonably talk about them together.
Of course, C++ offers you tools that C doesn't, but some of those tools have their own sharp edges as well. Plus, many C++ codebases are "C with classes" style or similar hybrids, those are still ultimately C++ programs, not C ones.
And that is the deal, lack of security culture.