compound annual growth rate (on average, what is bitcoin’s annual return over a certain period of time). in this case I believe the cagr is being measured over a trailing 4 year time period.

Bitcoin doesn’t have a CAGR. It is a measurement used in a fiat system that requires interest or dividends to be folded back into the principal over time as its fundamental mechanism. Bitcoins price is market driven with no interest or dividend payout. Applying CAGR to Bitcoin price is comparing apples with pairs at best.