Troubling fsck_hfs -Sd (block scan, debug) output. Help me understand. (PARTIALLY SOLVED)

I wanted to scan my backup drive for bad blocks, so followed a suggestion to do so with fsck_hfs.
I don't know what to make of the output of this:

18-03-04 MacBookPro% sudo fsck_hfs -Sdfy -c 16m /dev/rdisk5

journal_replay(/dev/disk5) returned 22

** /dev/rdisk5

Using cacheBlockSize=32K cacheTotalBlock=1024 cacheSize=32768K.

Scanning entire disk for bad blocks

Executing fsck_hfs (version hfs-366.70.3).

Block 2 is not an MDB or Volume Header

Block 7814037166 is not an MDB or Volume Header

volumeType is 0

0000:
0000 0000 0000 0000 0000 0000 0000 0000 |................|

. . .

01b0:
0000 0000 0000 0000 0000 0000 0000 00fe |................|

01c0:
ffff eefe ffff 0100 0000 d517 383a 0000 |............8...|

01d0:
0000 0000 0000 0000 0000 0000 0000 0000 |................|

. . .

01f0:
0000 0000 0000 0000 0000 0000 0000 55aa |..............U.|

unknown volume type

primary MDB is at block 0 0x00

alternate MDB is at block 0 0x00

primary VHB is at block 0 0x00

alternate VHB is at block 0 0x00

sector size = 512 0x200

VolumeObject flags = 0x01

total sectors for volume = 7814037168 0x1d1c0beb0

total sectors for embedded volume = 0 0x00

CheckForClean - unknown volume type

CheckHFS returned 6, fsmodified = 0

SORT OF SOLVED:

Looking again at the arguments I gave -

-Sdfy -c 16m

-d Display debugging information. This option may provide useful information when fsck_hfs cannot repair a damaged file system.

-S Cause fsck_hfs to scan the entire device looking for I/O errors. It will attempt to map the blocks with errors to names...

-y Always attempt to repair any damage that is found.

-f ... force fsck_hfs to check and repair ...

I am reminded that I included -d. (I entered the command a few days ago, and just saw the results.)

So I am probably looking at debug output that I can largely ignore since it ends in "fsmodified = 0" which suggests no bad blocks were found, and I pointed it at an entire drive (which isn't HFS+ by definition, rather than at an HFS+ partition on said drive).