!! Luna and I have talked about Hiro and Syaoran/Xiaolang knowing each other in middle school and being part of the same kind of robotics/tinkering clubs and working on projects together, so I think he could definitely know Sakura by proxy? They're only about a year apart iirc so it's not that much of a stretch. He probably would think she's nice enough but still not entirely know how to talk to her because she's way too pure (but he'd be friendly enough with her, and it gives us something to work with for the future.)

GOD SOMEONE SAVE SAKURA. Hiro would mildly feel bad but also he's gotta express himself =\ Sorry about him