CopyFit is wrapping lines (allowing a line of text to break to a new line)
CopyFit is designed to fit text into a text frame/box by adjusting any of the following formats: Tracking, Horizontal Scale, Point Size, Leading, Space Before and Space After.
CopyFit will not adjust any other character or paragraph formatting that has been applied to the text, including whether lines are allowed to wrap or break.
Therefore, whether a line breaks depends upon the formatting that you have assigned to the original text in the document and upon the size of the box containing that text, as well as the CopyFit parameters that you have selected to fit that text.
For those using the latest version of DesignMerge and CopyFit in InDesign, you can select the CopyFit Method named "Fit Line-Wrap". This method will prevent lines from wrapping (breaking) while shrinking text to fit.
For those using an older version of DesignMerge and CopyFit in InDesign, you can prevent text from breaking to a new line by assigning the No Break setting to a selection of text (the No Break setting is available in the Character panel menu or in the Control panel menu).
For more information about the various character and paragraph formatting features that are available in your page layout application to control line wraps or line breaks, please consult that application's documentation.