I can honestly see Kazumi crying either way - crying tears of sadness if Shana was chosen, and crying tears of joy if she was chosen.
So, that
alone would leave things open to plausible different interpretations, I think.
But Shana's smile seals it for me. I just can't imagine Shana smiling if Yuji chose Kazumi, or if he chickened out and chose nobody.
If Yuji chose Kazumi, Shana might cry a little bit herself - she certainly wouldn't be smiling.
If Yuji didn't choose anybody, I could see Shana getting angry and pouty and thinking "stupid Yuji!". Again, she wouldn't be smiling.
That being said, even I'll admit that JC Staff can contrive all sorts of things out of thin air - such as Yuji having never heard Shana say "I love you, Yuji." at the end of season 1.
So, it's not out of the question for there to be a Shana III, and for JC Staff to come up with some sort of lollerrific retcon to the Yuji chooses Shana or Kazumi scene.