They didn’t say “almost all”, only that there were many people who would. That seems highly plausible given how many millions of people have pirated content: no, it wouldn’t be everyone buying everything they’ve downloaded but even a modest percentage would be a noticeable increase in sales.

There’s a widely accepted claim that Netflix entering a market correlated with piracy going down because many people are looking for something to watch at a reasonable price. The person who is looking for, say, the latest release or determined not to support certain large media companies is probably still going to hoist the Jolly Roger but that’s far from everyone.