If the barrel and handguard between the LSW and DMR variants are the same, and the receiver and the rest of the rifle are also the same, then it is the same gun.
Compared to a standard rifle length QBZ-191, QBU-191 has longer, likely heavier barrel, new and longer handguard, possibly free floated. Those are all modifications that are as appropriate for a DMR as for an LSW.
So I could see the rationale for QBU-191 operating both as an LSW and the DMR role. Swap out the scopes and maybe even the magazine, and the gun can be equally viable in both roles, though of course a standard 30 round magazine is perfectly fine for the LSW role as well.
It wouldn't be dissimilar to the M27 and M38.