You can't verify anything internal unless you're internal or it has already failed publicly, so you of course have to draw on patterns seen elsewhere. Critical-process failures in one area correlate heavily with failures in others.
Plus, Epic has not exactly shown themselves to be producing consistent quality in anything related to their store, or many internet-connected properties. If they were, this might be more attributable to "accidents happen, it's impossible to prevent them all". It could still be an abnormality, but they're edging further towards "... maybe not though" territory.
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Edit: lets add a concrete "kinda example, kinda counter-example". Google is a tech company that is pretty good at consistently renewing its many certificates. They recently failed to do so for Google Voice: https://www.bleepingcomputer.com/news/google/recent-google-v...
I think there's a reasonable argument to be made that this reinforces claims that Google Voice is low priority / at higher risk of future issues due to lack of care, i.e. systemic issues, compared to other Google properties. I have no proof, but that doesn't mean it's automatically unreasonable.