And remember Ass-Face Roy and Joe Walrus from the Mon Eisley Cantina? Hooray or something, they came back in Rogue One!
This scene is similar to one later in the movie, when we see C-3PO and R2-D2 on Yavin, watching the fleet roll out.
This is weird, considering that they're in that very fleet in A New Hope. Fans have already done the mental gymnastics required to fix this obvious mistake ("They must have taken a shuttle later into the war zone, because that totally makes sense!"), but the obvious answer is that Lucasfilm simply wanted to shove these characters into Rogue One and didn't bother to think about it too hard. And hey, when this kind of nostalgia callback inevitably wears off, people will have to confront the merits of the writing itself, y'know?
And let's talk about the spinoff movies (like Rogue One) for a second. These could explore enigmatic side characters like Boba Fett, jump forward or back centuries, or even completely switch genres. Who wouldn't want to see a Star Wars noir-style detective film? There are so many amazing options ...