"Yes, we all know that you can have rotation and CBMP in the same movement. When you do so, the result is known as CBM. "
Which is true, but not at all what you'd expect after reading:
"The placing of the stepping foot, forward or back, onto or across the line of the other foot, giving the appearance of CBM having been used, but without turning the body."
For proof of the frequent confusion this causes, you need only look at past discussions right here - we've regularly had people mistakenly insisting based on that that CBMP steps cannot also have CBM.
But more importantly, the reason I maintain it's unecessary to bring this into the answer to a beginner question is that a beginner dancer does not need to know when to say a step can or cannot be considered to be be placed CBMP, they need to know what to do when an expert has written that it should be placed in CBMP.
They don't need to know what does and does not qualify for the term, they need to know what they should do when they read it. What they should do is place their foot across to the other side of their body. To find out if they should or shouldn't be turning (rotating) their body, they will have to look to other parts of the step description.