Any way to tell if the rosewood is quartersawn by looking at it? (see attached pic)
You can't call that either. When you take a section from a smaller log you get a mix of both flatsawn and quartered grain. Picture a slice going right through the center of the tree- the grain would appear as straight parallel lines. Flatsawn wood can have wild grain like you see at the outer edges of that back.
Nice back; what is the guitar?
It is a 2007 Blueridge BR 260, solid Brazilian rosewood. According to Saga they managed to secure a load of recovered tree stump Brazilian rosewood and made a limited run. It's not a Martin but at my age when a solid Brazilian rosewood guitar is on your bucket list for 20 years you get what you can. Here's a quote from one of Frank's YouTube videos "If you don't take care of Brazilian rosewood it will crack; if you take care of it it will crack. It's going to crack eventually". So my guess is this guitar will someday crack.
I was going to guess it was some of that stumpwood. Martin used some too, and from what I was told it cracked easily while being worked, and much CA was used to enable sides to be bent from it.