Reformat Mac SSD drive so fast - did it really work?
If the drive in question is an SSD then using the 7-pass erase option will not function the same way as on an HDD. On an HDD data is written by using a tiny, and very powerful magnet to flip the magnetic field's direction all over different parts of the disk, and smaller magnetic fields sometimes called "Ghosts" will be left after writing new data to the drive, allowing old data to be recovered by looking at what direction the magnetic field used to flow in. For this reason the 7-pass erase flips the field of the entire drive to the down position (or "0") from beginning to end 7 times in a row, to get rid of any lingering Ghosts. Plus on an HDD files are usually stored as a single stream of data, or in large chunks in only a couple of different places on the drive.

However, and SSD writes data by running a lot of electricity through narrow canals, causing the metal to heat up until the "bit" begins to melt. To stop all this excess heat from killing the drive an SSD writes each file in teeny-tiny chunks, scattered all over different parts of the drive, usually in a very random looking way. Since none of the files are actually intact as a single stream of data the way they are on HDDs, the only thing that allows the computer to figure out what files any of those tiny chunks of data belong to is the Partition Map, which is a record of where on the drive all the parts of a file are.

Basically, when you erase an SSD the only part of the drive that actually gets erased is the Partition Map, because without it to tell the computer where all the different parts of a file are the entire drive looks like a garbled mess of gibberish to the computer. This is why it takes so little time for your drive to secure erase 7 times over, the only part getting erased is that record of where files are, not the files themselves. Since that record is only a few hundred megabytes it only takes about as long to wipe it once as it would to copy a few hundred megabyte large file to another folder.

In the end you should also be careful when using multi-pass erase methods on an SSD, because the excess heat re-writing the same part of the drive that many times creates could be enough to damage it.