It's obvious stupidity in multiple ways:
They failed to account for the customer's long and positive track record. They must be having a CRM. About time they started using it instead of acting like a script that wakes up and shuts down without any context.
Despite being web and mail hosting experts, their architects failed to design their systems for the scenario that their critical mails end up in spam.
Their UX people failed to title the mail in a way that would grab attention.
The post says that apart from this single email and its 2 hour deadline, there weren't any notifications in the past, something that other people here have assumed without checking.
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In all such posts, it becomes obvious again and again that tech businesses are failing to design their systems for corner cases. This is not that surprising given all the communication and decision-making complexities anybody who's worked in tech would have seen.
Victim blaming is the laziest and most useless approach because it just denies that the real world is more complex than the ideal use cases the designers assumed. And neither helps improve anything nor holds anybody accountable.