Ok I am not sure how close or far off I am here and IF I am explaining this correctly... When reading sheet music is strumming a down stroke a single note line, and a UD strum when you see both notes attached? I can figure out IF in 4/8/16's BUT cannot quite catch onto the strum patters used, IF I could figure it out in sheet music I can of course figure the pattern out.
The rhythm shown is a fairly commonly used one, and often takes a bit of getting into.
Simple way to consider most strum patterns in 4/4 is that the 4 main beats (1,2,3,4) are downstrums. This of course means that the hand needs to go in the opposite direction in between, for the '&' part. You could strum all 8 down/up strums, and that would fill each bar.
Taking this principle, you're actually missing the strings on some of the movements down or up. 1 (&) 2 & (3) & 4 (&).