ACR ACFT TAKES ANOTHER ACFT'S CLRNC TO CROSS AN ACTIVE RWY.

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ON LNDG AT LAS ON RWY 25L THE CTLR HAD US EXIT AND HOLD SHORT OF RWY 25R. THIS WAS DONE. AS TFC DEPARTING RWY 25R PASSED US; I HEARD 'TFC IN POS WILL HOLD; CROSS RWY 25R; TXWYS D; AND S. I READ BACK THE CLRNC TO CROSS. THE CLRNC WAS ACTUALLY FOR AN ACFT DOWNFIELD WHICH I DID NOT KNOW ABOUT. THERE WAS NO CONFLICT. WE ONLY FOUND OUT THAT WE WERE WRONG WHEN THE CTLR TOLD US IT WASN'T FOR US. SUPPLEMENTAL INFO FROM ACN 464330: CONTRIBUTING FACTORS WERE BUSY FREQ; ACFT WITH SIMILAR SOUNDING CALL SIGNS (LAST DIGIT OR TWO THE SAME IN MANY CASES); CREW DISTR WITH RECONFIGURING; AFTER LNDG FLOWS; ADVISING PAX AS TO WHY WE WERE STOPPED. ALL THESE DUTIES WERE DONE AFTER WE WERE STOPPED WITH BRAKES SET AND HOLDING SHORT. CORRECTIVE ACTIONS WOULD INCLUDE A MORE DILIGENT EFFORT ON BOTH FLT DECK CREW MEMBERS' PART TO BE DOUBLY SURE OF CALL SIGNS; READBACK PROCS SHOULD ASCERTAIN BEYOND ANY DOUBT THAT THE CORRECT ACFT IS COMPLYING WITH THE CLRNC OR INSTRUCTION; AND THE CAPT BACKING UP OR ACTUALLY HEARING THE CLRNC NOT JUST THE ACKNOWLEDGMENT.