Originally posted by Raistlin

1. How Cloud actually got out
2. Why we don't know about it, as he's the main character
3. Why Cloud doesn't know about it, as when he was controlled later he still remembered.
4. The "2" tatoo Dio sees on the "black cloaked man" which seems to go with the Sephiroth clone theory.
Concerning your last question, the person Dio saw had tattoo No.1, No.2 belongs to the man in the pipe.
Plus... Dio speaks of this person who's about Cloud's age... but once Cloud wins the chocobo race to escape prison, Dio sends him a letter, which then states Sephiroth and him have spoken. Presuming 'Tattoo 1' guy is Sephiroth, why would Sephiroth come to the Gold Saucer, leave, then come back and talk to Dio?

Concerning Cloud escaping... I find it unlikely. For one, Tifa was in the room the whole time and didn't see or hear anything, not to mention that after they fell asleep, when they woke up later Cloud was sitting in the exact same spot as when he went to sleep.

Here's a totally random theory... maybe Reeve unlocked the cell? *very random*