It could be CF but it might not be. I don't have much experience of this, but my DD3 does have CF, and I have now met many other parents with children with CF and nobody has come across this situation.
Its no good saying try not to worry, because who wouldn't, but I hope your friend has good news soon.
I work in screening and this soft marker is a much contested one. Yes, on paper it may be that it is an indication of cf, but the vastmajority of cases when it is seen on a scan turn out to be nothing at all (ie. not ds, not cf, just a variant on the norm). Most reasons for EB are not either cf or ds - simply something that is noted but doesn't indicate anything clinically significant . I wish your friend well - have been there myself with 4 of my dcs at 20 weeks!