These people are all correct. This one is intuitive, and the problem only arises when people get "whet your appetite" confused with "wet your whistle", making these phrases only a bit less confusing than the "cut the mustard"/"pass muster" problem:

"*Wet your whistle' predates 'whet your appetite' by some centuries, and was first recorded in the 1386 Towneley Mysteries:

"Had She oones Wett Hyr Whystyll She couth Syng full clere Hyr pater noster."

Whistle here means throat or voice and the phrase just means 'take a drink'."

This explanation is brought to you from http://www.phrases.org.uk/meanings/whet%20your%20appetite.html