I doubt that it is true.  C++ was originally released by AT&T as a preprocessor
to the C compiler; their compiler generated C code.  There's nothing in the
language that makes it inherently less efficient than C.  Of course it's easy
to use all the baroque bells & whistles in C++ or bloat your program by
linking in
all the libraries but one can write an unreadable or bloated C program
(check out how big a printf("Hello world") program is).

The worst part of C++, in my mind, is that it offers too many non-essential
but alluring gizmos which trip up newcomers to the language.  Of course, this
is true of other programming languages as well.

Ben