Two thoughts:
1) Bryan is pretty explicit that those are volume recommendations per session, and the Wernborn review didn't look exclusively at bro splits afaik.
2) It is plausible that there is a growth threshold that is reached by doing enough work at enough weight in enough time. So what happens if you don't reach that threshold?
For example, if you had a beginner do a ~10 RM three times a week per lift, you'd expect that person to increase in strength and size, yes? What if they did 1 rep of that 10 RM 10 separate times over the day? You could say "they both did 10 reps (the same workload) at their 10 RM in a given day," and conclude they should be comparable for growth. The reality is the 10 separate singles probably wouldn't do jack and ****, because it's not nearly high enough of a "right now" stimulus to achieve much of a training effect.
Same deal for weekly volume. If you just look at "volume per week," you may be missing the fact that growth is happening/not happening on a per session basis. I mean, growth happens for ~24-36 (up to 48) hours after an acute bout, right? In order for that to happen, you have to do enough, at that time, to trigger that. I think it's entirely plausible that if you fail to cross this acute stimulus threshold, you aren't going to grow, even if the "weekly volume" adds up to be the same.
Note also that that famous study looking at 9 sets of leg press once per week vs. 3 sets 3 times per week was used in novices, part of the basis for our ideas of partitioning out our workload. For them, 3 sets was enough per-session to trigger growth. What happens if 3 sets isn't enough? Eventually, the 9 sets guy is at least growing once per week, and the 3 sets 3 times per week may be growing zero times per week. If these particular numbers seem unrealistic (3 sets is still a decent amount), imagine it's 3 sets once per week vs. 1 set 3 times a week (e.g. how most people run the 15's), and the trainee in question is intermediate/advanced.