APCH CTLR ISSUED AN AMBIGUOUS CLRNC AND MLG HAD ALT DEVIATION WITH POTENTIAL CONFLICT.

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WE WERE FLYING THE BOIDS 9 ARR (DFW BPR BOIDS 9) IN AN MLG. OUR CLRNC WAS TO DEPART BOIDS (BPR 108 DEG R/13 DME) HDG 100 DEGS; INTERCEPT THE DFW ILS RWY 13R LOC; DSND TO 5000'. AS WE DEPARTED BOIDS AT 5000' AND BEGAN SLOWING FROM 250 KTS TO 210; WE WERE INSTRUCTED TO SWITCH TO 118.1. ON 118.1 THE CTLR TOLD US TO FLY 090 DEGS TO INTERCEPT THE ILS; MAINTAIN 4000'. I READ BACK THE CLRNC; SET THE ALT ALERT TO 4000' WHILE THE F/O SET 090 DEGS IN THE HDG SELECTOR AND INITIATED A DSCNT TO 4000'. AS WE DSNDED THROUGH 4300' THE CTLR ASKED WHERE WE WERE GOING AND SAID MAINTAIN 5000'. THE F/O STOPPED THE DSCNT AND I ADVISED APCH THAT HE'D CLRED US TO 4000'. AT THAT TIME WE SAW AN SMT Y COMMUTER ACFT AT OUR 1 O'CLOCK POS AT 4000' AND APPROX 4-5 MI. THE SMT Y WAS NBND; RPTED US IN SIGHT AND MAINTAIN VISUAL SEP. HE CROSSED ABOUT 3 MI IN FRONT OF OUR NOSE. WE CONTINUED TO 4000'; INTERCEPTED THE ILS FOR AN UNEVENTFUL LNDG. BOTH THE F/O AND MYSELF; AS WELL AS ANOTHER PLT IN THE JUMPSEAT; BELIEVE WE WERE CLRED TO 4000'. I CALLED THE APCH FAC AND THE SUPVR ON DUTY HAD ALREADY TALKED TO THE CTLR INVOLVED. BECAUSE THE WX WAS VMC; AND SINCE BOTH ACFT CREWS SAW EACH OTHER AND WERE ABLE TO MAINTAIN VISUAL SEP; NO FURTHER ACTION IS BEING CONSIDERED. THE CTLR INVOLVED DID SOUND A LITTLE UPSET BY THE EVENT. (THIS HAPPENED DURING AN ARR COMPLEX THE DAY FOLLOWING THE ACR DEP ACCIDENT.) THE POTENTIAL FOR A SERIOUS ACCIDENT DID EXIST.