Legos are manufactured from plastic. Most plastics are derived from oil, if I remember correctly. A side by side chart comparing the value of lego sets versus the price of oil could make for an interesting contrast.
Plastics are polymerized organic compounds, but for the life of me I can't remember if they're still making plastic from any of the hydrocarbons found in oil. You'd think scientists would have figured out a cheaper way to synthesize the various forms of plastic without the use of crude oil byproducts.
I don't think a Lego vs. oil price chart would tell you much, because while oil has fluctuated wildly for many years, Legos that you could buy on the shelf of your local department store probably just rose with whatever the inflation rate was at the time. The article is talking about Legos as a collector's item, and that has nothing whatsoever to do with the price of oil. I'm not surprised that there's a market for them among collectors, but I don't know how long that's been a thing.
All in all you clearly cannot count Lego as a "store of oil/plastic value", there are way cheaper means for it, from the Lego clones to most the old/torn sports clothes.
No, that's what I was pointing out in my post above. It's possible that if the plastic Legos are made of is indeed made out of oil that their price might go up a little if oil were to skyrocket, but I don't think there would be much correlation between the two things if you were to compare prices over at least a few decades. And as jackg is also pointing out, the high price of Legos only goes for genuine Legos, because for whatever reason people want them, and they want the real thing and not some Chinese counterfeit or knockoff.