If bitcoin were truly exponential, then we would already be at $1 million a coin since this chart predicts the future. The "winning the lottery" like returns on bitcoin are over now, which is what garnered mainstream interest in the first place. You'll make more on some random shitcoins than bitcoin now, in lottery like returns that is.
What do you mean by "truly exponential"? There are an infinite number of exponential functions that can be defined: ex, e0.5*x, 2x, 3x, etc. just to name a few. One can dream up and curve fit a number of exponential functions to Bitcoin's price data over time. OP is curve fitting the data to some exponential function from 2011 to 2021 (which is linear on a log scale).