But I saw people dancing West Coast Swing and it looked nothing like what I learned?
Well, there are two possible reasons for that. West Coast Swing is a constantly evolving dance that is always getting more diverse, more ergonomic, and more fun. Unfortunately, this makes it hard for most local dance teachers to keep current, so their material and teaching methods get outdated quickly, which means their students do too. You may have learned WCS from an outdated source and the dancers you observed were current, or vice versa. The other possibility is that you may have been watching dancers from another area of the continent dancing a regional style of WCS.
Is there competition? Do I have to be really good to compete?
There are competitions available for every level of dancer - newcomer to pro. You only have to know your basics, which means you could compete after 6 weeks of training or 6 years! You are only ever competing against people of your same level. As you get more advanced, there are competitions for choreography, but it's all optional.
I have lots of technical dance training. Is this an advantage or disadvantage?
This is an advantage. Anyone who tells you otherwise doesn't have the training to communicate to you exactly HOW. It is a common misconception that ballet and jazz will "taint" or "ruin" your ability to learn Swing. That's a load of crap. Just like university teaches you how to think (regardless of the subject area), dance training teaches you how to manipulate your body (regardless of the dance style). In short, dance training will make you a quicker learner. Yes you will have some habits to change, but that is the case for all dancers, trained or not.