Well I upgraded to Pro about two days later, so maybe the upgrade did it? But either way, there was absolutely zero indication that the drive is getting encrypted or that it's going to save my recovery key to my Microsoft account.

It's called "device encryption" which seems to do the same thing and they allow it for Windows 10 home. It's confusing.

It's bitlocker but only activates if you log into a MS account in which case it:

* silently activates

* silently sends the key to MS.

And this is the only way to have it on home.

Ah. Which is probably what happened to me as I've signed into my MS account.