Too Short REALLY CONFUSED -- Did I Get a DUI???

Rapper Too Short literally has no idea what happened this morning ... because on his way out of jail, he couldn't figure out what the hell he was arrested for.

We spoke to Too Short moments after he was released, and the rapper was utterly baffled by the booking sheet in his hands -- which only listed a felony narcotics possession charge.

Too Short said, "I thought it was a DUI. This says possession ... I'm confused, man."

Fact is ... cops tend to book people on the highest charge -- in this case felony narcotics possession -- and then leave the remaining charges to the D.A.'s office, however it decides to prosecute. In other words, Too Short could still face a DUI charge in addition to drug possession.

TMZ broke the story ... Short was arrested early this AM in L.A. on suspicion of DUI and narcotics possession, after he was pulled over for some traffic violation ... and allegedly took off running.