Exactly.

It is unhealthy, but the data doesn't say that.

I don't see what the difficulty is. The data measured weight loss, and he lost weight, and cholesterol improved as a result of reducing meat. The data didn't measure digestive function, fat versus muscle, bone strength, long-term risk of cancer of the colon, scurvy, or any of the things we'd expect this diet to affect. If these had been measured, then the data would have supported the claim he wanted to make.

For LWers there's no story here.