It is funny when we distinguish the thumb from the fingers – I mean, it is one of the five. There isn’t always a good reason for it – but in this case – Hamlet’s right, when you play the recorder, your thumb does something quite different from the other fingers. Look at this – Hamlet and Shakespeare giving ACTUAL instruction on recorder playing.
Of course – if this were the only instruction you had for how to play the recorder, you probably wouldn’t get very far.
Ventages is a fun word for holes, though.