I would have guessed seeing one product sold out would make other similar not-sold-out products less appealing. Like, if brand A is sold out but not brand B, I'm going to wonder what's wrong with brand B. Is it inferior in some way?
If you're set to buy brand B and brand A is sold out, you probably don't even notice it. But if some variations of brand B are sold out (like some colors, one of the examples in the article) than maybe you might commit to the purchase.
Anecdote: When I was looking to buy a Keychron K2 it was sold out, both standard and premium model. I was set to buy the standard model, so I asked to be notified when it was back in stock. First to get back in stock was the premium model, I chose to wait it out. Next day I got an email offering a 10% discount for the premium model - the standard model was still out of stock, so I bought the premium model.
I'm happy with the purchase, but that circumstance made me spend 10-15€ more for a nicer keyboard: out of stock standard model + price discount.