Both can be correct, as they check entirely different things.
SMART measures operating parameters within the drive, such as temperature, numbers of transient read errors, head flying height, speed stability, etc. When these fall outside expected values, it flags an error die to the likliehood of imminent failure - normally due to mechanical problems. Thus SMART is a forwarning of a failure to come.
ScanDisk and Disk Doctor merely read/write to the disk and check essentially for surface defects - they don't even take into account raed errors - if ta block can be read it says it's OK, even if it takes several tries to read it.
All disk manufacturers accept SMART errors as a valid reason to make a warranty claim.