That is correct. They just wrote data over the whole damn disk. ATA SECURE ERASE as I believe directs the controller/firmware to bring the cells to a factory state, which takes a little time because the cells only need to be marked clean, not rewritten or anything like that.

The method I use on my SSD when reinstalling:

    hdparm --user-master u --security-set-pass 12345 /dev/sda
    hdparm --user-master u --security-erase 12345 /dev/sda