He didn't choose to leave - he was deported. He also didn't choose to not come back - he's on a blacklist for 5-10 years.
What Thai prisons are like is irrelevant since the guy in the article did not spend any time in Thai prison. Going by the info in the linked article - he was arrested and spent a day in Patong police jail before being granted bail. He was free for 6+ months in Patong, then a couple of months ago, in May, he pleaded guilty on his court case and given no additional jail time - only deportation. He then had to return to Patong police jail where he waited a week to be transported to Bangkok Immigration Detention Center. He spent about 2 months in the IDC before the embassy were able to schedule his flight out. It's certainley not pleasant, and I'm sure the IDC feels like prison, but between that and "I almost died in Thai prison" there's quite a leap.