100% the drive had a read error.. But it appears to have rewritten to the same sectors no problem, with out having to reallocate a spare
From the SMART report
rror 1 [0] occurred at disk power-on lifetime: 32365 hours (1348 days + 13 hours)
When the command that caused the error occurred, the device was active or idle.
After command completion occurred, registers were:
ER -- ST COUNT LBA_48 LH LM LL DV DC
-- -- -- == -- == == == -- -- -- -- --
40 -- 51 00 00 00 01 16 e5 1b 60 40 00 Error: UNC at LBA = 0x116e51b60 = 4679080800
I'd keep an eye on it, but don't worry excessively right now.