An SSD has no concept of "files"
It doesn't know an NTFS filesystem from an Oracle database, everything is just blocks.
They would have needed to add some ability to understand an NTFS filesystem for it to see if a bunch of files are replaced with identically named files of the same size within a short period of time. I can't really see any other way it could determine a "ransomware attack".
While false positives would be possible, I doubt many people do such encryption in place where they encrypt a bunch of files without changing their names in some way to reflect that new status, so this is probably fairly safe in most cases.
If this became a standard feature on SSDs it would be easy for ransomware to avoid. Buy one of the SSDs, reverse engineer how the algorithm works, and work around it. Maybe they can only encrypt a few files at a time, then do some other "make work" tasks to create and delete other files, then encrypt a few more, etc. It would take longer, but this runaround would only happen on an SSD so it would still be much faster than when ransomware attacks an HDD based system.