ALTDEV ALT EXCURSION CREATED BY CLRNC INTERP CONFUSION DUE TO PHRASEOLOGY AND TRACON APCH CTLR TECHNIQUE ATC COM.

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DEPARTING SMX CLRED DIRECT RZS DIRECT OXR; MAINTAIN 9000 FT. ZLA SWITCHED US OVER TO PT. MAGU APCH ABOUT 30 MI FROM OXR. WE WERE DIRECT OXR AT 9000 FT PT. MAGU CTLR WAS BUSY WORKING MULTIPLE FREQS. WE WERE ABLE TO CHK-IN AND ASKED FOR DIRECT NELLY (A FIX ON THE ILS RWY 25 OXR). HE SAID HE WAS UNABLE TO DO THAT FOR TFC. THEN AFTER TALKING TO OTHER ACFT HE SAID 'MAINTAIN 7000 FT; STANDBY' AND WENT QUICKLY TALKING TO ANOTHER ACFT. NORMALLY I READ BACK CLRNCS AND RPT LEAVING ALTS. HE WAS VERY BUSY AND SAYING 'STANDBY' MEANT TO ME; HE DIDN'T WANT A READBACK AT THAT TIME; BUT I SHOULD COMPLY WITH HIS INSTRUCTION TO LEAVE 9000 FT FOR 7000 FT. AT 8500 FT HE ASKED WHY WE'RE NOT AT 9000 FT THEN SAID MAINTAIN PRESENT ALT. WE MAINTAINED 8500 FT AND SOON WERE CLRED (AGAIN) DOWN TO 7000 FT. ALSO WHEN WE INITIALLY CHKED INTO PT. MAGU APCH HE ASKED OUR ASSIGNED HDG INDICATING HE WAS UNAWARE OF OUR NAV (WE WERE DIRECT TO OXR). THERE WAS NO TFC CONFLICT BUT I FELT THAT ISSUING AN ALT FOLLOWED BY THE WORD 'STANDBY' IS NOT A GOOD PRACTICE BY A CTLR. DOES IT MEAN STANDBY WITH READBACK OR STANDBY WITH EXECUTION OF ATC CLRNC? OTHER CONTRIBUTING FACTOR: HIGH WORK LOAD FOR CTLR.