This is a feature of email clients like Mac Mail on MacOS or Mail on IOS etc.. Once a message is received in your inbox, the email client and services like Siri evaluate it and may add items such as calendar events or flights as tentative entries.

You can either change the Siri settings on your devices to prevent this behavior, or increase your spam filtering so those messages never reach your inbox.

With the addition of SpamFoo in our environment, we no longer have a substantial number of spam messages in our inboxes, so I've re-enabled some of the automatic suggestions for calendar events and flights across my various operating systems and apps.