Can 4NT be "incontrovertibly not artificial" ?

Another more interesting insufficient bid from Devon!

W	N	E	S
1S	2H	X	3H
X	4H	5D	P
4NT
5NT

North pointed out that 4NT was insufficient, and West said something like "oh dear, well I can make it good" and bid 5NT, someone suggested it wasn't as simple as that and the TD was called. I (the TD) decided that I should talk to West away from the table, and she told me that she intended 4NT as natural (to play). I decided that I would err on the side of allowing the auction to continue, prepared to fall back on Law 27D if the other side were damaged. So I ruled that if North did not accept 4NT, the correction to 5NT must stand (Law 27C) but would not silence partner. I thought I was ruling under Law 27B1(a) that 4NT was "incontrovertibly not artificial" but perhaps I was ruling under Law 27B1(b) that 5NT had "the same meaning as" 4NT.

5NT ended the auction and was destined to go off. I told the table to call me back and left the table.

But it's never that simple.

I returned to the table to point out that if I had ruled that 4NT or 5NT was artificial, then East would be silenced anyway. Meanwhile, West had explained that there had been a misexplanation. The first double had been explained as take-out, showing the minors, and the second double had been explained as take-out, equal length in the minors; but West had intended the second double as penalties. The misexplanation did not appear to damage North-South but I guess there was heaps of unauthorised information.

I repeated my instruction to be called back but I heard no more: I guess 5NT went off.