I’d find it unlikely that 500,000 people would download an app expecting to buy a share while the market is closed, but if you do, fine, let them leave their review.
I can easilly believe that people genuinely downloaded and signed up in the expectation of buy GameStop/Bitcoin/tulips or whatever this weeks craze is. When they find it doesn’t work (because the backend didn’t scale or because the app maker decided not to sell tulips) they’re are genuinely annoyed.
This isn’t people downloading the app just to rate it 1*, based in the hype it’s quite possible these reviews are all genuine customers.