It's boilerplate text. Since it is a TATL itinerary they will protect on Lufthansa group

For a schedule change/market suspension such as PRG, unless they arranged a specific protection agreement with another airline for the city pair, it will only be on LH group, not any *A. Schedule changes require agreements between the airlines to accept rebooking under the existing fare (even among *A carriers) or otherwise the rebooking airline is liable for the prevailing fare. IRROPs do not require those agreements as those are handled under different settlement standards so they could potentially do any *A (or even non *A) in that situation (still JV preferred).