Speaking a foreign language in a dream when you know next to nothing?

My friend sent me an email relating the following tale of dreaming in Spanish, even though he's studying Japanese and knows pretty much no Spanish. I'm not exactly sure what to make of it, so I'll throw it out to you. What do you think?

My mom asked me this morning what I was dreaming about last night because I was talking in my sleep. I couldn't remember anything so I just shrugged it off and asked what was I saying? Here's the kicker, my mom said "You were speaking Spanish. It was like a conversation going on for a few minutes." I was even doing it with a Spanish-like accent. I can tell you flat out that if hard pressed to say more than please and thank you in Spanish I would drown in a sea of my own ignorance. Also, as you know, the only Spanish I ever took was in high school, with Mrs. Huggins, which I never even opened the book for, so I wouldn't say I learned anything that could subconsciously be festering in the back of my mind. I have never been to a Spanish-speaking country, don't listen to Spanish-language music, rarely watch Spanish films (and definitely not recently), and have had no other interaction or exposure to Spanish-speaking people recently. So where does it come from?

My friend throws out a few of his own ideas, after the jump.

The first thing I thought was what does my mom, whose Spanish knowledge would be even less than mine, consider a conversation? Was I repeating myself a lot? Was I mainly speaking gibberish with a Spanish accent? And so on. So without concrete evidence that I was speaking understandable Spanish, it's hard to say the extent of my subconscious knowledge. But she DID say I was speaking complete sentences, waiting—as if listening to what the other person had to say—and then responding to them. When asked how she knew it was Spanish, she said 1) it sounded like the stuff on Telemundo or from the Feliz Navidad song (which, being Christmas, is probably my most recent exposure to Spanish), 2) she recognized "sí", "señorita" and "gracias" within the sentences I was saying, and 3) she knows Spanish just well enough to pinpoint it, but doesn't understand a word of it.

I really wonder if in learning Japanese, I've triggered some other language linked neural path that just happened to surface as my long ago Spanish exposure, or if I'm absorbing Spanish unknowingly through tidbits of passing exposure that's being tucked away because it is recognized in my mind as a language I've cognitively learned in the past? Quite interesting stuff if we can gather more info on it. Maybe I'll have a graduate thesis in here somewhere.

My best guess? He was dreaming in Spanish, but it was limited to whatever he knew and was enough to fool his mom, but if a Spanish speaker had been there it would have sounded like some poor imitation of Spanish. Although I have to say it'd be pretty cool if there was some font of incidental knowledge of languages picked up here and there that we could somehow tap...