In that it claims certain things are "common misconceptions"
while the text is formulated in such a way as it might
create a new misconception about Open Source vvs. Free
Software (That Free Software is not also Open Source??).

Specifically in that same paragraph where it says...

"and avoid common misconceptions : the
Linux kernel is not the GNU/Linux
operating system, commercial software is
not necessarily proprietary software and
Libre Software (Free Software) is not Open Source."

I.E.
Libre software is Open Source by necessity. If it
were not Open Source, then it could not be free.

it should read the other way... that "Open Source software is not necessarily Libre Software"

Here's what I think the whole thing should say instead:

"and avoid confusing use of terms/nomenclature.
For example, in referring to the Linux Kernel, and the
large number of operating system distributions based on GNU/Linux: don't call everything "Linux", be specific.

We're talking about names, not misconceptions...
common misconceptions are like: "strncpy guarantees
NUL-termination of the target" (it does not),

or "Windows XP SP1 is more secure than windows '98",
etc.

Commercial software is not necessarily proprietary
software, and a lot of Open Source Software is NOT also
Libre Software (Free Software), they are different ideas."

An uncommon misconception is much worse than a common one,
because people won't expect it, and will cause even more
confusion than a common one. At least with common misconceptions, you can learn about them, and be sure to
ask what people are talking about (to be sure)

A codified misconception is even worse than an implicit one, because it creates the an illusion of authority behind the misconception.

-

There's no Operating System/distribution called "GNU/Linux" either, that seems contrived. "Debian GNU/Linux" or "RedHat Linux" are OS distributions, for example. If one wants to refer to the Linux-kernel-based OSes in general, most people say Linux, it's certainly easier to say, and is what the public mostly calls it.

Lack of understanding, probably, misconception, not really,
you have to know what a kernel is before you can confuse
other things with it. People want convenient nomenclature, and GNU/Linux or "Linux Kernel" do not roll off the tongue very easily.

sp. It just happens that people are Lazy and use confusing terminology

Since nomenclature is by convention, it's not necessarily misconception when people refer to the "Linux OS", either (sigh)...

at which point your best option is to task them what they meant precisely whenever they said "Linux OS" "Kernel" or "Distribution"

-Mysid