Defender - Am I getting a False Positive?

So I received a scary email alert today:

Hi Ben,
I come bearing news of an immediate threat!
I have detected your site on The Black Lists of Google. Specifically, you are on the Request Timeout.
To fix this issue, I recommend following the guidelines in Google’s own knowledge base articles:

When I scanned the site with Sucuri and looked further into it, I am not in fact on any blacklists as far as I can determine.

So why did this happen?