Bard has traveled from Aiseth, so he's not a local. I imagine the festival probably draws a lot of merchants, so he has probably been working for one of them as a porter or something similar. He's very poor, has no claim to fame, and probably doesn't go out of his way to attract attention. I'm not against him having seen Talia around the market...  I imagine she'd be kind of hard to miss, but he's probably too straitlaced to have crossed paths with thieves or elves. Yet. Possibly he could have told off an unwanted suitor that was harassing her while she was shopping?