He may be referring to coins from Uncirculated/Brilliant Uncirculated/Proof-Like sets. Until just the last few years these sets were struck with different finishes from the one used for Circulation coins. So an MS65 Circulation coin is an uncirculated Circulation. Where as an MS65 taken from a set may be referred to as Uncirculated (note the capital). There's a section in Charlton Vol 2 (which I lent out and haven't gotten back yet) on the sets and you see them change over time from Proof-Like to Brilliant Uncirculated etc as the mint changes their production. I believe ICCS currently identifies the Brilliant Uncirculated sets as Numismatic BU. You see this in Charlton Vol 1 as the price charts show PL65 in the 50's & 60's but MS66 NC (Noncirculating) in the 80's and 90's and then nothing at all for 2011+. Be aware that many sellers use many of these terms interchangeably but the value of an MS65 vs an MS65 NC is quite different. The first is uncirculated (Mint State) while the second is Brilliant Uncirculated (Mint State).