Correlation is calculated using specific data at specific times and is a mathematical equation. It's not about graphs and empirical observations.
Markets are too complex to be measured and analyzed using math and equations. If it were otherwise, anybody could become ultra rich writing some simple equations and an automated script that trades and generates them a massive income.In fact, Bitcoin and the S&P500 (US market) are astonishingly highly correlated.
I honestly don't see actual correlation here, specially when we have these.2x rise from 2015 to 2016 <=> a small drop in S&P500
a big crash from 2018 to 2019 <=> a small rise in S&P500
a big rise from 2019 to 2020 <=> a small drop in S&P500
The only correlation bitcoin has is with the global economy so when for example the 2020 pandemic damages the global economy with recession, the effects are seen in bitcoin market as well with a crash. Other markets are obviously also affected by the global economy and they also crash. But that doesn't mean just because Bitcoin and S&P500 are crashing both, there is a correlation between the two!