From my metallica bass riffs book (don't sue me Lars....)
the bass follows the guitar, so:
|--3--|--3--| |--3--|--3--| |--3--|--3--|
-------------7-------------7--------------7
0-0-0-0-0-0-0 0-0-0-0-0-0-0 0-0-0-0-0-0-0
d-u-d-u-d-u-d d-u-d-u-d-u-d d-u-d-u-d-u-d
With this in mind, and what you've posted above, I'd be inclined to say the last notes of each 7 note group consists of a down-stroke chugg on both the E and the A string simultaneously, with the last of the triplets you noted in your post being an upstroke from the A to the E string.
Does that make any sense?
One thing I do know for certain - Hetfields right hand downstroke riffing is mean as
****... the second intro riff (the one to four fret stretch one on the E & A string) to master of puppets is all done with down strokes on the guitar. I played the bass part to that with my fingers, so rolling from one string to another with my middle and index finger was easy.
So it's entirely possible he played it with all down-strokes.
Can you see how they do it on their first music video (which just happens to be One).
https://youtu.be/8NhKK8Y-wIo you can kind of see the strumming pattern at the end, but it's not real close. Could be all down-strokes on that last note - would make sense for the E & A string to ring out like that whilst muting the D string.
Having said all that, if you watch hetfield closely all the way through you do see him Up-stroke in the fast section after 'landmine has take my sight' etc
So perhaps the part I outlined above ends with a down-stroke, but the part you show ends with an upstroke?
*derp* my brain hurts now