I've talked to Seagate. I'm forwarding their response in hope it will
benefit others with the same problem and doubts.
The Short Test of Seatools is not as accurate as the Extended Test of
Seatools. We mainly rely on the Extended Test for most-accurate results.
You may visit our support website for more information on the DST error
code you are receiveing, but if you are not receiving this error code
under the Extended Test routine then you have nothing to worry about.
DST Error Codes
00 No Error
01 DST was Aborted by User
02 DST was Interrupted by Reset or Power Off
03 DST Could Not be Run
04 DST Failed for Reasons Unknown
05 DST Failed Electrical Element (Read/Write Head Check)
06 DST Failed Servo Element (Track Following Check)
07 DST Failed Read Element (A Bad Sector was Found)
Seagate Technical Support
Thank you all again for the excelent smartmontools!