He said "they shipped computers with a 10% throttle on their GPUs". And that does not mean anything. That's not a thing,

He is either talking about the power limit, he oversimplified the story so much it makes no sense, or he has no idea what he's talking about.

And no, you don't need to touch the clocks to adjust the power limit, that's not how it works. You can adjust the power limit on it's own just fine, all it does is limits how much power the GPU can use. Your GPU adjusts it's clockspeed automatically. The power and thermal limits are what tell it how far to go. If you lower the power limit, the card won't boost as high. But it doesn't mean there's a 10% hit to performance. It might be that 90% power is enough to get you 99% of the performance. Depends entirely on the card.