I don't know about different visa types or what type of visa this guy has but for the Thailand Elite visa they are quite specific on the application forms - if you've been sentenced to more than 1 year in prison for any crime other than negligence then you're not permitted to get the visa.
I guess if you've been sentenced to less than 1 year in prison at any point in the past then it's no problem.
However, there is no way they can check this as they don't require a 'police report' so you just sign the form which I guess is a legal declaration - I imagine if they later found out you had indeed done a decade or so in prison then they might kick you out and revoke the visa.
I wonder if something similar happened here.
Is there any similar kind of declaration for retirement or other types of visa?