Well a 'command set' implies a set of functions, 1 command per function. So if you increase the command set, you've increased the number of functions, which means they added something new to the TRIM command.
What that might be, I don't know. Going by his description, it sounds like they managed to implement some detection of non-allocated cells, which would allow them to re-allocate said cells without actually copying junk data to the new location.
IE the system decides that block 105 is under-used and 657 is over-used. Normally this would involve copying what's in 657 to 105 and vice versa, but rather than blindly copy 105 to 657, it detects that block 105 isn't actually allocated(the file that was there has been deleted or something), so it just assigns the mapping from 105 to 657, saving a write.