"Went down a Treat"

Do you know what this means?  I just received a message from a customer in the UK that a necklace she purchased "Went down a TREAT."  I read this and didn't understand it, Did she miss a word in the sentence?  Did the necklace fall off while she was baking cookies?  Did someone accidentally take it while Trick-or-Treating?  So I decided to Google it and here is the definition of the phrase: "It was enjoyed very much." 

Phew, I'm so relieved...

Here's RJ eating 6 cookies worth of cookie-dough...they went down a treat!