Here are some direct from the source help pages that might clear up your understanding of the system. https://support.google.com/google-ads/answer/156066 https://support.google.com/google-ads/answer/6167118
From your first link, "how relevant your ad text is to searches, how likely people are to click your ad, and the quality of their experience once they reach your landing page"
This is all data that's generated based on the overall learning that Adwords does against your site presence. It's why it takes weeks to really get your data settled in, and why if you (or your Google rep) start to mismanage your account, things will rapidly go bad.
Maybe it isn't causal? But the correlation is pretty near 100%.