You had RAID1 mirroring in place, one of the drives failed 14 days ago. Failed hard enough for the card to stop writing to it, but no so hard that it wouldn't actually work when you tried to read/write. But since it was marked as failed, your RAID card would no longer touch it. Then, 14 days later, perhaps in response to another issue, you took out the other (more current) drive and replaced it with a blank one.
Since your failed drive hadn't been written to in two weeks, the data was two weeks old. That's what you synced over to the fresh drive, which is why it looks like your server hasn't been used in two weeks.
Presumably your OTHER drive (the one which didn't fail two weeks ago) either
A: is still good and can be used to recover your recent data, or
B: also failed, albeit more recently and perhaps with more severity
A single disk failure in RAID-1 is not catastrophic, and therefore caries no inherent signs of distress. Your computer just keep chugging along on the remaining good drive. Unless you're actively monitoring your RAID array, you won't know about the failure until the other drive fails as well, which will cause the server to crash (no working drives left).
Some RAID cards will reset the fail/good flag on a drive after a reboot under certain conditions. It's stupid, it happens.
This sounds a lot like what happened to you.