I would agree. The chocolate tin is the same one in the past. And Nishida is the only one around Yuuki, so Nishida put the tin in his bag, I'm guessing, the same one he used in the past. I'm guessing his name is different because maybe, and I'm not too sure, because I can't think of another reason, (actually I can but that one is sad) Nishidas parents got divorced so he changed his name. (I don't want to think that he had a brother that was hospitalised and passed away, or something ridiculous like that.) But yeah I agree totally that Nishida is the guy on the other end of that tin.
It's also what I think: Yuuki's friend, the same tin and the divorce of Tohru's parents to explain the change of name.
I also thought of Tohru's death when I was reading the chapter but I don't think it's that either.
I also noticed that we've known the full name of Yuuki and Tohru (in 2010) but we've never seen the first name of Nishida (even if we can guess it's Tohru), althought Nishida calls his friend Yuuki. Yuuki should also call his friend by his first name, not his surname.
I think that Nishida has already said his first name to Yuuki when they first met but Yuuki is used to call him Nishida and has not made the connection yet.
It shouldn't take Yuuki a long time to guess though because there're a lot of clues: when he asked for a phone call, he had Nishida; when he gave him his address and ask to see him, Nishida was here; Nishida have known for three years where and when he could meet Yuuki and he knew his face, etc...
I already know it. His real life friend is the guy who writes the letters in the tin