If he's right, it's going to be news to a lot of people.
He's talking straight out of Fiction Fitness magazine. I'd say the majority of coaches here at T-Nation recommend hitting the same muscle group several times each week (Chad Waterbury has suggested up to 4 times a week).
It's all dependent on what you're doing each session, and what your goals are. If you're doing the exact same workout on Monday, Wednesday, Friday, and Saturday, then no...you won't get any better. But if you vary the reps/sets/weights each time, you'll get further.
So, you can certainly train the same muscle group multiple times each week.