CAPM - SML or the CML

Not sure how this question affects the SML instead of the CML:

“According to the CAPM, if investors borrow at a rate that exceeds the risk free rate, the resulting borrowing portfolios will plot a flatter line”

Not sure how this affects the SML instead of the CML. I thought the SML affects different securities on the line, while the CML affects different compositions of one portfolio along the line.

As such, I feel like this statement pertains more to the flattening of the CML instead of the SML.

It does.