"i'm not a you, i'm a me!" - is it normal for kids to do this?

Here's a typical conversation between a teacher and I in primary school (some time between the ages of 6 and 8).

Teacher: "E, you need to do this"/"You are being funny[or whatever other adjective]"
Me: "I'm not a you, I'm a me!"

* * * * *

I found it incredibly confusing whenever a teacher tried to talk to me using correct grammar and I could NOT understand who on earth this 'you' was. Anyway, I think that's how my mind worked at the time.
Oddly enough, I wasn't saying it to deliberately answer the teacher back.