If you had no form of propulsion you are a NUC. As you had engines and were not anchored you were under way. Drifting is considered underway by USCG.
If you drift into another, (IE anchored) vessel, you are at fault, as you are moving, and they are not. Prop wash will close the gap between a powered vessel, and another vessel, due to law of physics, faster moving fluids have less pressure than slower moving fluids.
In this case you drifted into another vessels path....As they likely didn't know whether you were drifting, or just slowly maneuvering, (no day shapes?), usual collision avoidance rules were in effect, Ie passing, crossing rules. When you failed to comply, they should have given you a wide berth.
That they failed to do so indicates they were also paying more attention to the race, than surrounding traffic.
Lesson for future; When not at anchor
in an accepted anchorage, have someone at the helm, and on watch at all times.