I don't find it surprising, especially for someone that is already a musical prodigy. I remember dreaming of beautiful melodies as a kid, but lacking musical talent, I was unable to play them on a musical instrument. Thus, the melodies were just stuck in my head and usually forgotten shortly after waking up.
The thing is, RDJ is legendary for self-mythologising. As a result of this, everyone else mythologises him too. He's obsessed with messing with his fans' heads. He has openly stated in interviews that he lies about himself all the time.
To be fair he could have written that stuff as a teenager. But then maybe he also owns one of Kraftwerk's original vocoders, modified to produce output in Cornish.
Apparently he also has a lookalike that walks around at his shows to divert the attention of fans.
