Just a comment... when the bet was made, Subaru was in his formal Sumeragi robes ^^ It'd be hard to mistake him for anyone else.
Actually, I think Seishirou does mention in TB 7 that he didn't know that Subaru was of the Sumeragi clan. I'll double check my translations again. But the only reason I remembered that was because I thought the same thing you did ^^ (Honestly, who else would he be?)
Thank you so much for your sweet review! I'm so sorry I made you cry! ^^;;