Results aren't very surprising. At a 3RM, intensity is greater than at a 10RM, so each individual rep will potentially have a greater impact. But you won't be able to do as many reps in a set, so you'll need to do more sets. Because each individual rep is at a higher intensity than when using a 10RM, it makes sense that you wouldn't need to match volume rep for rep to get the same amount of hypertrophy, however a significant total volume is still needed to match results. So 7x3 eliciting the same hypertrophy as 3x10 is nothing unexpected.
Many will treat this as sound rationale to do low rep training for the explicit purpose of hypertrophy, because "it's just as effective." What they forget is that 3x10 with 90sec between sets and 60sec for each set is only 6min of training, whereas 7x3 with 3min rest between sets will take 3 times that long just to sit around -- then there's the actual lifting on top of that. Where two methods are equally effective for the task of building muscle, the one that can be achieved in less time is the more efficient option, and thus superior.
Of course, if the goal is to build max strength, it's pretty common knowledge that sets of 1-5 will be more imminently effective than sets of 8-12, so there's nothing new here on that front.