Is KAIST really as high pressure as it seems?

Got accepted to KAIST for Master's. I'm from Canada. My other option is Yonsei Songdo campus.

I was reading through the KAIST Herald and they mention bad cafeteria food, people wearing lack of sleep as a badge, and just overall being super overworked and under pressure. I know this might be a symptom of the whole country but when I studied abroad at Yonsei, I found there was a good balance between work hard and play hard (eg extracurriculars).

I'm considering going with Yonsei to network and build my own company during the Master's instead of slaving away to research at KAIST - would this be the worst idea? Anyone in KAIST Daejeon that can speak to what school culture there looks like on a day to day basis?

Mind you I messaged my prospective KAIST lab prof (who accepted me to his lab weeks prior) some questions around his expectations, freedom in choosing a topic, etc. and he freaked out and told me to choose the other program (Yonsei) instead. What now?