Perfect move, that's exactly the smart way to race at a track where a bump draft works. It's also helpful if you need to catch the draft ahead, and have a car behind... slow down to let him catch your slipstream and then work to catch the car ahead with that bump draft energy.
You hear it said all the time during NASCAR races at Talledega... they have to 'back up' to let the car behind catch up and then bump draft ahead. The leader will often do just as you did... ease off the throttle to let the car behind close, because at 100% throttle and parity with the car behind, you become a sitting duck.
Well done!