from PADI Manual:
Conduct and Standards
You conduct all portions of the Waterskills and Stamina exercises in confined water, except the Diver Rescue Assessment and Development, which may be conducted in confined water or open water.
was that swim in Open Water? Or is that considered confined water?
On any of these stamina tests, remember, go slowly to start, get your rhythm, it is an aerobic activity, going fast to start will make it an absolute beahhtch
play with streamlining; I find that hands in front I go faster - I also use Mares Avanti L fins and I can scoot pretty well - just watch your calves and arches for "shark bites"; best to stretch before starting to help w/that