If you're writing software, and you develop a new feature without testing the failure path, then I don't think it's possible to make any safe assumptions about what failure should or shouldn't do.
I agree with you on general basis, but in this case it seems that Stripe provides a dashboard containing key data. It's not unreasonable to expect that critical payment failures would be displayed as well.
It's always a risk to make assumptions, but I don't think this specific assumption was unreasonable.
