I just watched the movie yesterday!
There are some plotholes with the meeting, but it could have happened.
My biggest issue is, S1 he says the accident was when he was 6. He's 18 and she's 14 in S1. So she was 2?!?!. Which, a)I think Usagi and Shingo are farther apart in age than that, and b)why would a two year old be walking alone, no less talking like that and what not.