It's a fairly new hypothesis, comming out of recognition that plant oils with exception of olive oil, maybe some others, are fairly new thing in human diet and their usage (as replacement for animal fats) kind of correlates with raise of modern diseases and obesity.

There are also some molecular pathways that might be triggered by substances in plant oils but there's not much systemic research into this yet.

But I think it's all plausible. There's really no harm in restricting yourself to just olive oil out of all extracted plant oils. And since it cuts out most processed foods available on the market it might help you on other ways.

You can still eat plant oils with the whole plants they come from becuse you won't be able to eat even remotely close quantities of them this way.