Scandisc shows how readable the actual data is. If it's green then the drive was able to figure out the data 100% if it's yellow then the drive had some trouble reading the data and had to slow down and work harder on the ECC to fix the missing data. If it's red I think it means the drive was unable to read any usable data in that section of the disc. The other scan shows the disc's physical condition as in the actual bits, rows, blocks. Chances are there are lots of rows with errors but the data you were writting was moved to another set of bits that could be read properly or the drive was able to correctly guess the missing bits of data using its ECC allowing you to use 100% of the data. Either of these 2 cases will give a green result in scandisc. If an entire row is deemed damaged then you'll see a yellow or maybe red mark in scandisc and the data will.
In short data corruption will show up as yellow or red in scandisc and disc surface damage will always show in the quality tests as PIF or PIE or POE or POF.
PI is Parity Inner which refers to Parity data at the end of every row of data and PO means Parity Outer which refers to the parity data at the end of every block of data. PI Errors are any row that has at least 1 byte of of errors. PI Failures is when there's too many consecutive rows of PI Errors. PO Errors are when there's too many rows in a data block of errors (consecutive or not doesn't matter) and PO Failure is the big fatal one, if there is even 1 POF your whole disc is no good and pretty much unreadable (you'll need a data recovery program to get the data or drive with superb fault tolerance). A POF I believe is when there is more than 1 CONSECUTIVE POE that or is a larger number of consecutive POE.