I don't think the graph is still relevant, in 2017 most projects are ERC-20 tokens, that's why the money flowing in ETH since the project need to have gas fees. But nowadays, most people don't like ERC-20 tokens anymore due to high fees, it moved to BSC and now it moved to SOL.
But it's only outperform in that time.
I don't understand what you actually meant by ETH outperforming Bitcoin when we know that Bitcoin dominance of the market is still above 51% while ETH has 16%. There's still a huge gap.
I think he meant if ETH price increased higher than Bitcoin price in terms of percentage, ETH outperform BTC. But it's only outperform in that time.
That's only his opinion based on analysis, I don't see it in reality of Bitcoin market right now. The huge difference of eth and btc price is hard to break, if there's a probability of altcoin season for next coming months then we will wait and see. Predictions is hard to foresee, performance of altcoins is still getting more interesting for most holders and with positivity I think everything will follow in perfect timing.