FLC OF B757 ON TAXI OUT THOUGHT THEY HEARD A CLRNC TO POS AND HOLD. THERE WAS NO QUESTION IN THEIR MINDS UNTIL THEY HEARD CTLR INSTRUCT A LIGHT ACFT TO GAR.

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AT TUCSON; THE FO AND I WERE COMPLETING A TAKEOFF BRIEF AND THOUGHT WE HEARD POS AND HOLD. AS WE TAXIED ONTO RWY 11L WE NOTICED A SMALL ACFT WAS INSTRUCTED TO GAR BY TWR. AS WE CROSSED THE RWY LINE; THE CTLR TOLD US WE WERE CLRED INTO POS AND HOLD FOR RWY 11L. SMALL AIRPLANE WENT AROUND AND WE WERE GIVEN CLRNC FOR TAKEOFF. IT APPEARED THAT WE PREMATURELY TAXIED INTO POS AND TWR STATED THAT THERE WAS NOT A PROB AFTER WE APOLOGIZED FOR THE CONFUSION. UPON REACHING DFW; WE CALLED TUCSON TWR AND SPOKE BRIEFLY WITH THE CTLR WHO DIDN'T SEEM TO BE TOO CONCERNED WITH THE SIT AND THAT THE SMALL ACFT WAS DOING AIR WORK TO THE W AND DID NOT INTEND TO LAND AT TUS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT THE MAIN REASON FOR THE PROB IS THAT ON TAXI OUT THEY RECEIVED A COMPANY CALL STATING THE POSSIBILITY OF A DOOR NOT SECURED. THEY PULLED OFF TO SIDE OF TXWY WHILE A TRUCK CAME OUT TO INSPECT THE DOORS AND THEN GAVE A THUMBS UP. DURING THE PROCESS OF GETTING BACK INTO THE FLOW OF TFC AND COCKPIT PROCS BOTH PLTS THOUGHT THEY HEARD THE POS AND HOLD CLRNC. SINCE BOTH HEARD IT THEY DID NOT QUESTION THE CTLR.