But it could be if they were using the Concise Oxford Dictionary, which is the one I quoted... Which is bigger.

In any case the second meaning given in the Compact version doesn't imply anything about excluding planning in advance. "Open, natural, and uninhibited" sounds an excellent way of summing up a good session.

Anyone got a fullsize Oxford Dictionary, or access to its website?

Howevere that wouldn't settle anything - I'm sure that it would show that the word has been used and is used in a range of meanings, like any number of words are. That's why words get re-defined for particular legislative purposes.