Just selling altcoins for BTC, fiat or any other coin doesn't belong in Currency Exchange. The quoted rule is referring to threads that offer exchanges between fiat and BTC in addition to other exchanges (e.g. BTC to alts, alts to fiat, etc.).
I maybe be a bit dense today, but I don't understand what you are trying to say (sorry). If the currency exchange board is not meant for just exchanging coin A for coin B (being A or B Bitcoin), what is it for?
The Currency Exchange board is meant for exchanging BTC to fiat currency. If within your Currency Exchange thread you offer to sell or buy alts for BTC / fiat / other alts
in addition to offering to buy and / or sell BTC for fiat, that's allowed
1. However, if you're only offering to buy / and or sell alts for BTC / fiat / other alts, that thread belongs in Marketplace (Altcoins).
1 If a user is trying to circumvent the restrictions by mostly making a thread about exchanging alts while only adding a token mention of trades between BTC and fiat, a moderator may opt to move the thread to Marketplace (Altcoins).