He was the lower a/c on approach and the PA28 driver had the onus on him to maintain seperation....
That's not necessarily true. Weight-shift microlights have a very high rate of decent for approaches. Although a microlight may clearly be Number One, he probably won't be above a fast fixed wing a/c for the same time period before landing.
This really muddies the issues at an uncontrolled airfield, as the rules of the air state that the lower aircraft has priority - not the one who was establish first - even if they are gliding in!