That wasn't very nice of your neighbor to say.
Yours looks like a full yorkie to me. But my Aunt bought a Yorkiepoo...and paid a ridiculous amount of money for her and she now looks exactly like a purebred yorkie.
Yours is very cute and looks prurebred to me. I'd find out if I were you...I've heard of the DNA tests...not sure how much they are. If you bought a purebred Yorkie puppy and I know they can be pricey, then you should find out. Do you know your neighbor well? Is he/she an experienced dog person??