Is it normal for professors to twist the truth about their labs?
I think your perception of twisting the truth is correct, but I wouldn't call it lying if this is your interpretation. The twisting of the truth is more produced among professors and group leaders by students that don't know exactly what topic they are interested in exactly and should pursue for PhD work. I think you are a in a minority, burning for a exact topic. At least when you don't have to pay for your PhD work, but have a salary, my impression is many PhD students choose their department/group/topic rather based on criterions like salary, infrastructure, need to move, location and culture than topical or research-related criterions. 

Group leaders need simply good people to work in their labs, and they are looking for really good people or mediocre with very much hands-on experience for a distinct project. A group doesn't act like a company with very specific job description. You need a team that is able to develop and learn, as science never stands still. Maybe your professor wants to go more into NLP and finance in future. Especially young group leaders have to dive also in new topics and broaden their scope. So this you should discuss with him. But in general his "approach" is right to make you interested in his group and not deliver you reasons on a silver tablet to not join him.

If there is too much truth twisting can and should also be proven by you. Good groups hava a good publication track and often an alumni section on their website. This is something I would always throw an eye one before talking to group leader. What research did he 5 years ago, last year, how much people work on distinct topics and has the group many collaborators and of which quality? 

The group may currently not work on your topics, but have a better infrastructure than other groups to work on it. This is something you have negotiate and outline with the professor before starting any contract, in best case by a binding research proposal, so there are no misunderstandings for what you will get your PhD and work on mostly.

That competition and working pressure is really high in south korea is not unknwon, as suicide and emigration rates of academics to have an easier life. 

I'm not sure why often professors are here on the academia.se treated as holy cows or responsible for everything. No researcher is trained to become a professor like a surgeon, it's learning by doing and they are humans like everybody else with personal inadequatnesses. They are no own species like it often sounds here. If the truth is twisted a lot, then it is rather a problem of academia at your university or country or the general culture. Of course professors are in competition to get good people, like everywhere else outside of academia.