This cound mean a couple of different things.

S.M.A.R.T. can be enabled and disabled on the fly, by both the BIOS and software. The BIOS cannot prevent software from enabling it, though. Except..

Modern drives often implement DCO (Drive Configuration Overlay), which is a way for a BIOS to selectively disable certain drive features, and have the drive no longer even report that those features exist. hdparm --dco-identify can give information about this.

The DCO modifications can also be frozen with a command from the BIOS (or from software, for that matter), such that a full power-cycle is required to regain access to deleted functionality.

Cheers