Yes, they were using 1 oz 1375 fps steel loads but you can read the research for yourself on that topic. In the past, I also shot and killed some pheasants with 20ga 1 oz loads of #4 steel but I'll let the research speak for itself on the pellet size topic, here is one quote from the article link.
"Bagging vs. wounding
Of the three loads tested, No. 2 steel exhibited the highest B-1 bagging rate over all distances, at 76.9 percent. No. 4 steel was second at 65.7 percent, and No. 6 steel came in at 62 percent.
At distances of less than 40 yards, where the hunters in this test, when not constrained to fire at certain distance increments, took most of their shots, 86.5 percent of birds bagged with No. 2 steel were B-1, dead or immobile within 30 seconds. At less than 40 yards, No. 4 produced a 73 percent B-1 rate, and No. 6 produced a 75 percent B-1 rate.
What that means to hunters who need to make a choice between steel shot loads is that of all birds bagged, No. 2 steel produced a higher percentage of clean kills than the other two steel shot sizes tested.
The other side of the equation is wounding loss, or birds visibly struck by pellets but not retrieved. All pheasant hunters have lost roosters that "hit the ground running" because the bird was not centered in the pattern (a nice way of describing shooter error), or perhaps because pellets did not penetrate to vital organs. All pheasant hunters who use steel shot and want to reduce the potential for crippling loss can tilt one factor in their favor by choosing No. 2 steel whenever possible.
Of all birds struck with the No. 2 steel load, 108 were retrieved and 10 were lost, an 8.5 percent wounding loss rate. No. 6 steel produced a 13.6 percent wounding loss, and No. 4 steel came in with a 14.3 percent wounding rate. Interestingly, hunters lost only two of 68 birds hit at distances of less than 30 yards with all three loads combined, a wounding rate of 2.9 percent. All test loads together produced 15.1 percent wounding loss at shot distances of 40 yards or greater.
For the entire test, wounding loss was 12.2 percent. "That's a pretty low wounding rate," Roster noted, especially when compared to findings of 15 shotshell lethality tests on waterfowl, some of which examined both lead and steel. Trained observers in those tests detected 30 percent or more of birds hit by hunters with either shot type were not retrieved."