Buddha's Birthday

Today, 16 May, is a public holiday. It should have been on 15 May, but that was a Sunday this year, so they made it Monday. We've had quite a few public holidays the last two and a half months: Good Friday (25 March) and Easter Monday (28 March); Ching Ming (清明節), known locally in English as Grave Cleaning Festival (5 April); First of May, (2 May, because 1 May fell on a Sunday this year). The more the merrier, I say.
So what's it today? Buddha's Birthday.
The historical Buddha, Siddhartha Gautama? Or any of the other before or after Buddhas? I haven't a clue. And I don't think anyone else does either, or cares.
But I do know: this public holiday was one of the results of a long series of talks. The talks between London and Beijing prior to the handover of Hong Kong in 1997. Talks on items big and small. Item: the public holiday marking the occasion of the British Monarch's Official Birthday. That would have to go. Evidently, they were also in accord that the number of public holidays should remain the same (remember: one country, two systems).
My guess is that since there were already public holidays on significant Christian and traditionally festive Chinese days, some bright spark, or sparks, suggested something non-contentious, like Buddhism. Hey presto, Buddha's Birthday! Then they moved onto the next item on the agenda.