Well I haven't seen a poem written in the first person before. I don't know if this is supposed to be a limerick or not. I kind of missed the joke. (Sorry I thought this form of poem was meant to be funny. If it's not, I apologize.) If I were to give my honest opinion this is more like a ballad.
However, my nitpicking aside , this is a well written poem. You can definitely feel a rhythm when you read the words.
I feel that this is a heartfelt remembrance of a dear companion. I'd side with the professor from University of Iowa. This isn't plagiarism. Your words were yours and the subject, while still a dog, was YOUR dog not Jimmy Stewarts.
This is the best slice of life story I’ve read. I like how George and Jeff bonded over video games. Some authors might say to avoid adverbs but you made them work for you instead of having you work for them. Well done!