SMART health-test and status

I have an external USB-drive which is giving me the following output on running the command $ smartctl /dev/sdb -H on it: SMART Status not supported: Incomplete response, ATA output registers missing SMART overall-health self-assessment test result: PASSED Warning: This result is based on an Attribute check. Could you elaborate if this is something to worry about or if it is just a wrong setting? Generally, what is the meaning of the health status in simplified form? Maybe as a relevant aside: The short and long tests finish without issues.