There are a few possible reasons for this mistake basically. If you look at how the classes are usually laid out in the files, it is Soldier, Scout, Scoundrel, Guardian, Consular, Sentinel. It's entirely possible that someone assumed that the middle entry would be the Sentinel, because it is the compromise option in the final game, without seeing that it was actually the Consular.
If I had to take a guess though, I would say that the consular and sentinel originally filled different roles. If you think about it, it makes no sense that Bastila is Sentinel and Jolee is Consular. Bastila has now practical skills, and her entire shtick is how powerful she is. Jolee on the other hand, was a smuggler at one point, and clearly isn't a super force user. The descriptions in game for the classes are also bizarre. The consular refers to mental disciplines and augmenting the force all the time, while the Sentinel is dedicated to rooting out evil and striking balance. If I had to guess, I would say that the consular originally got 3 skill points (compared to the guardians 1 and sentinels 2) and used lots of skills but sucked at combat (using skills to augment the force). This is entirely speculation, but I think it makes a lot sense. At some point they realized this was stupid probably, and took away the consulars skills because no one wanted to play a sentinel under those conditions. This meant that the sentinel was originally a literal hybrid like the scout, instead of the more bard-like class in the game now.