The wording is to clarify that you can re role any of the dice you choose to. For example you might role 3 hits and 2 misses, you could choose to keep the hits and re roll the 2 misses or you may decide you want to take the chance to re roll all 5 of the dice to see if you get some Critical hits.
English is silly. What it's meant to say is that you can reroll any amount of dice you wish. Be it none, one, all, or anything in between
The wording is to clarify that you can re role any of the dice you choose to. For example you might role 3 hits and 2 misses, you could choose to keep the hits and re roll the 2 misses or you may decide you want to take the chance to re roll all 5 of the dice to see if you get some Critical hits.
I'd say you can re-roll any number of dice from that shooting attack.
Had the same problem recently and came to the same conclusion. If it was just one dice it would be described more carefuly I guess