Did I get a correct ruling?

[campboy]

If someone makes an insufficient bid then it is possible that he did so thinking the auction was different, but it is also possible that he did so because he got confused and thought it was legal to respond 2♦ to 2NT, or to bid 1♣ as an overcall of RHO's 1♠.

 

Playing with bidding boxes, in my experience at least 90% of insufficient bids fall into the second category.

 

Here there is additional evidence that the original problem is in the second category (the failure to announce, which I already pointed out). It is admittedly pretty difficult to get confused about what level a club overcall of 1♠ needs to be, but it is also pretty difficult to mistake a 1♠ card for a pass card, so I wouldn't like to put money on that one either way.

[bluejak]

OH, maybe because I thought you were aware 1C is not an overcall of anything and that the pair is playing a 16+ 1C opening bid style. My mistake.

It is quite clear from many years of directing plus many years of playing and making ludicrous mistakes myself that some IBs are made because the player bid at a lower level than either he intended or he thought was necessary to overcall the last bid.

 

Any TD who assumes that the reason for bidding 1♣ over 1♠ is because he missed the 1♠ and intended to open 1♣ without checking is

1. naive, and
   
2. not doing his job properly
   

[dkham]

An IB might come from picking up the wrong bidding card, or from not correctly noticing a previous bid. You can't tell which without asking.

 

So it's possible the 1♣ overcaller in bluejak's example thought he was overcalling 2♣, or the 2♦ responder in the original problem thought he was opening the bidding.