that's interesting. i like reading things like that that get your mind going, trying to understand how that works. i rarely do iso work, but it is surprising that the addition of iso's didn't have an effect.
so maybe if you wanted to train tri's and bi's, a better option would be lighter weight compound movements? like if your working sets on bench were with 250 lbs., maybe you could drop some weight, work with a very close grip, and do more presses (for tri's)? i wonder if this means that it's working with heavier weights that stimulates growth, not so much total volume. of course, it's also just 1 study.