Let me reassure you that a properly administered cleansing enema will not result in anything like 'enemas can make the lower . . . um, I kind of forget, but rectum, maybe? "balloon out" '
What the author probably was referring to was the sigmoid section of the colon that is just above the rectum, and where cases of severe constipation can result in a fecal impaction that can cause a baloon type situation that shows up clearly on an X-ray from a lower GI series.
But it's not the enema that causes this, it's the constipation, and relieving the constipation is essential if you want to restore the normal muscle tone to the colon.