ACR WDB RESPONDED TO WRONG CLRNC AND CROSSED ACTIVE WITHOUT CAUSING ACR B TO ABORT TKOF.

Narrative

HOLDING SHORT OF RWY 1R ON TXWY M AWAITING CLRNC TO CROSS FOR DEP ON RWY 7. ACFT WAS FACING APPROX 240 DEGS ON TXWY M. I HEARD A CLRNC TO CROSS THE RWY AND ACKNOWLEDGED SAME. THE CAPT TAXIED ACROSS THE RWY ON MY WORD THAT WE HAD BEEN CLRED. WHILE XING; I LOOKED DOWN THE RWY AND AT FIRST SAW NOTHING BECAUSE OF THE HEAT WAVES RISING. AFTER A MOMENT OR TWO; AND WHILE ON THE RWY; I SAW AN ACFT ROLLING TOWARDS US. THE ACFT WAS DISPLAYING NO LIGHTS AND I ASSUMED THAT IT HAD LANDED AND WAS ROLLING OUT. WE SAT SHORT OF RWY 7 FOR 5-7 MINS AWAITING DEP CLRNC AND NOTHING WAS SAID ABOUT CONFLICTING TFC TO US BY THE TWR. WE WERE CLRED ONTO THE RWY AND THE TWR REMARKED; CASUALLY; THAT WE HAD CROSSED W/O CLRNC. I REPLIED THAT GND CTL HAD CLRED US AND I HAD ACKNOWLEDGED SAME. POSSIBLY; I MISUNDERSTOOD GND CTL. BUT; NOTHING WAS SAID WHILE WE WERE XING THE RWY OR FOR THE PERIOD WHILE WE WERE WAITING DEP CLRNC. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR SAYS HE THOUGHT HE HEARD ACR A XYZ CLRED TO CROSS 19L AND ANSWERED WITH THE FULL CALL SIGN AND REPEATED CLRNC. APPARENTLY AN SMA SOMEWHERE OF ARPT POSSIBLY CLRED TO CROSS RWY 19R AND RPTR SAYS HE MAY HAVE HEARD AS CLRNC FOR HIM. DID NOT KNOW CALL SIGN OF SMA. TAPE PLAYBACK REVEALED THAT ALL OF WDB READBACK EXPECT RWY 19L WAS STEPPED ON APPARENTLY BY THE SMA ANSWERING. ANGLE WDB WAS HOLDING PRECLUDED THEM FROM SEEING BACK UP THE RWY UNTIL THEY HAD TURNED TO CROSS RWY 19L. FAA IS INVESTIGATING THE INCIDENT AND HAS THREATENED THE PIC WITH PENALTY. SUPPLEMENTAL INFO FROM ACN 91320: WHILE I WAS REVIEWING THE DEP PLATE I THOUGHT I HEARD; 'CLRNC TO CROSS.' WHEN I LOOKED AT THE COPLT HE WAS IN THE PROCESS OF STATING; 'ROGER XYZ; CLRED TO CROSS.' AS WE STARTED ACROSS I LOOKED DOWN RWY 19. WE OBSERVED AN ACFT HEADED TOWARDS US; ALTHOUGH AT THE FAR END. SINCE IT WAS DISPLAYING NO LIGHTS AND DECELERATING; WE ASSUMED HE HAD LANDED AND WAS CLRING. WE WERE WAITING FOR TKOF CLRNC APPROX 7 MINS W/O ANY COMMENTS FROM THE TWR; WHOSE FREQ WE HAD SHIFTED TO AFTER XING RWY 19. THEN; ALMOST AS AN ASIDE AS WE WERE GIVEN CLRNC TO TKOF; THE TWR OPERATOR STATED; 'YOU FORCED ABC TO ABORT WHEN YOU CROSSED RWY 19L.' IT IS POSSIBLE THE COPLT MISUNDERSTOOD GND CTL'S INSTRUCTIONS; BUT WHEN HE ACKNOWLEDGED THE CLRNC NO ONE CORRECTED HIM. WE CANNOT UNDERSTAND WHY SOMEONE DIDN'T IMMEDIATELY CONTACT US AND ATTEMPT TO DETERMINE WHAT WENT WRONG.