Indeed Bran would be level headed but I doubt he takes Sylvia's words seriously but he out of politeness (or tactful social thinking) does not address it. As he thinks this is indeed ploy by Matt but he sees a honest silver but as he does not know origins of said silver he is hesitant to make deals when there is trickery involved. He could very well suspect Matt had got fake silver coins just mess his head up with bribing one the guests join on his oppoturnistic prank (even if lying to be Aes Sedai is rather suicidal but could be viewed as innocent prank in back water village like Two Rivers). However Sylvia did mess his head already with her subtle natural domani ways :P. Anyways as note Moirane had not advertised at all in her journey that she is Aes Sedai and had kept her ring hidden as you both may have noticed. But Moirane now holds briefing session with the two accepted about what she is doing here.