Did I just screwed up my zpool?

[Bidule0hm]

A new drive should be tested before using it to avoid infant mortality: https://forums.freenas.org/index.php?threads/building-burn-in-and-testing-your-freenas-system.17750/ and https://forums.freenas.org/index.php?threads/how-to-hard-drive-burn-in-testing.21451/

 

[Robert Trevellyan]

Could the 2nd drive failed right when I tried to replace the 1st bad drive?

Yes, it's possible, especially with the specific 3TB Seagate model you have, which is known for sudden, early failure.