Really Jimi?

There is this song that is supposed to be Jimi Hendrix. It's called Happy Birthday, not the one we sing before you blow out the candles, but an original. This recording doesn't show up on any Hendrix albums, but it does appear on some bootleg compilations that have surfaced over the years.
The Beastie Boys sampled it on Check Your Head, for their song Jimmy James.
I've always just excepted it as a Hendrix song, until recently.
I put this song on a CD for some of my co-workers at the Fetus, and they question it being Hendrix on vox, and on Guitar.
Take a listen, and let me know what you think, or what you already might know about this.

Jimi Hendrix(?) - Happy Birthday.mp3 (zShare)

Zach Galifianakis - You Bring Me Joy