Not in RNA. The U he was referring to is Uracil.

Yes... I agree

Well in his defense, uracil rarely pairs with adenine because RNA is usualy single-stranded. There is double-stranded RNA, but it's very unstable and usually only lasts a couple milliseconds. Oh, and on the anticodons of tRNA molecules that are trying to build amino acid sequences. But again, usually doesn't pair.

dsRNA is broken down by dicer into siRNA to prevent the production of polypeptides by breaking down mRNA before it can be translated by ribosomes and tRNA

Yes, but what does that have to do with the fact that adenine in tRNA pairs with uracil on mRNA that actually does make it to translation?