Off the top of my head:
Bitcoin was around $1k in 2017 and, after jumping up to about $20k, was back at around $4k in 2018. It's recently been over $100k, and fairly reliably been over $40k for much of the time in-between.
Gamestop's share price was below $10, stock split-adjusted, for many years, bottoming at $1 ($4 unadjusted). It infamously rocketed to over $100 ($400) in January 2021, with several similar, seemingly-random bursts of upward volatility since. Even now, depending on your entry, buyers from before the high would have seen somewhere between 200% and 2000% returns. There are a number of other so-called "meme" stocks which briefly performed similarly, though most have not retained even a fraction of their increase.
Both could have been used to hit $2m or more with a single set of buy-sell transactions. That's not considering leveraged trading like options. Keith Gill infamously turned $50k (briefly) into a billion dollars (and is likely, more durably, a centimillionaire).
In short: crypto and options, buying early and holding long. 2017 was actually almost the perfect time to jump in. Someone who was looking in the right direction could easily have struck oil, as you say. (Let's not even talk about the guys who made $660m off the negative oil price incident in 2020.) ZIRP and lax oversight of the securities market structure make odd things happen.