Have I invented this statsitic on Theravada enlightenment?
This inference of the amount of attainments seems unsubstantiated. Those Thai monks are also split into factions where one will hold that Buddha lives in Nibbana and be in disagreement with others. All the factions can not be considered as equally valid traditions with right views, likely to produce the four types of contemplatives. There seems to be relatively little consensus on matters of doctrine among the Theravadins.

If you look at buddhist forums you should readily see how much disagreement there is and things aren't much better in the monastic circles afaik. From what i've seen there is usually a demand for conformity of views, at least in the small communities whereas the larger communities will tolerate a broader range. If one is ordained in one tradition one may or may not be considered to have a valid ordination by others.

The assumption that 1:1m can be a Buddha, if that is what you expressed, i don't know how you inferred it but we are about 7billion+ nowadays and the general consensus is that there has only been one Buddha in the last 2600 years. Furthermore nobody is expected to attain Buddhahood any time soon. Based on this alone one could assume that it is far more of a rarity than 1:1m.