That is a standard blues riff.
Really? I've never heard it played quite like that on any other
record. Still, I don't think 'originality' matters to some people -
as long as they're honest about the lack of it, I don't mind!
I suppose the problem is that some people believe if they acknowledge
all their sources, it weakens their case to be identified as the
composer.
I don't think it's the case in all traditions - for example, in reggae
it's quite common to have a version with only minor adjustments put
out under a completely different name and title. I think the
assumption is that if you like music, you'll know where the original
came from. Like the organ part on 'Double Barrell' by Dave and Ansell
Collins, which is quite clearly lifted from 'Lay Lady Lay' by Bob
Dylan.
Cheers
Daniel