You may want to go too the lore forum. That's where most of the lore masters hang out.
This. Looks like it got moved, nice.
Don't take the UESP as absolute truth, since anyone can edit it. I'm pretty sure that Hjalti (Tiber's original name) was Dragonborn, since he came up to the Graybeards and wasn't shouted to dust.
The Tiber thing is a whole lot more complex. In short, Talos is a deity created by mimicking the murder and usurpation of Lorkhan back during creation. This mimicry (called "enantiomorph") requires several actors - in this case, Tiber, Wulfharth, and Zurin. Though Tiber was the physical form of Talos, they are all part of that god.