Technically Frank hadn't written to him anything about the Order, and if it weren't Frank then hey that was a perfect window. So, there was nothing wrong or crazy about an auror wanting to mentor someone was there? Sirius wasn't going to bring it up, even if they were somewhere more secure than the cafe, and hopefully it gave him a better idea for who Frank was. But who would he corroborate that it was Frank with? Soon journals or charms was the main way to go. Owls could get intercepted. Hmm, James knew the Prewetts, and maybe they knew Frank?
"Who wants to sit inside on a day like today?" Sirius asked with a grin. He wasn't about to apparate anywhere with the man, but hey, there were too many ears here. Sirius had already ordered the large size of the sandwich when Frank spoke up. Sirius wasn't used to freebies from strangers, other than the Potters, but he didn't really expect needing it. Uncle Alphard had given him a lot of money, something about not having children and such, but even Sirius knew it wouldn't last forever.
"Thanks, mate," Sirius smiled. Food. Free food. It was a good afternoon. And Frank wasn't providing the food - that mattered.