Although I am not claiming to be right here, opening a 6 card minor as a weak 3 level bid so often proves fruitful.  Here, if I do not open, partner will open some variant of a strong 2 (for us, 2♣ followed by a 2N rebid).  After this, it is very hard to go on above 3N - with more info from the off, Alan was able to assess the slam possibility (well done Alan!)