That is absolutely correct.

For applications requiring simultaneous writes from multiple programs (concurrency) or ACID transaction properties, using Markdown files as a substitute for a database is undoubtedly an anti-pattern and entails a risk of data corruption.

You're absolutely right ... and this is more for a personal database (the way most people use Notion).

Strictly we could have titled this: the markdown database pattern for small personal databases.

The point was that for personal use e.g. keeping a list of projects, or books etc this is perfect. Or even for maintaining this list on a website.

It isn't for multiple simultaneous writes