Best example I can give is a post I saw a while back where someone was trying to remember the name for a manta ray and described it as a sea pancake instead. Logically you could call it a sea pancake and most native speakers will get the gist of what you mean, but the actual name is still manta ray. Is there a word for that sort of phrasing in writing when you use nonstandard language but it still gets the point across or works as a valid name/descriptor?
Expressing one thing in terms of another, which is what your friend seems to have done, may be put under the umbrella of 'kenning', per the Oxford English Dictionary:
One of the periphrastic expressions used instead of the simple name of a thing, characteristic of Old Teutonic, and esp. Old Norse, poetry.
*Examples are oar-steed = ship, storm of swords = battle.
The term is adopted from the mediæval Icelandic treatises on poetics, and is derived from the idiomatic use of kenna við or til, ‘to name after’.*
Wikipedia has a very detailed and apparently scholarly article on Kennings, which I have linked to above. It isn't very quotable and I can't vouch for its accuracy at all, things are more simply put at YourDictionary.com:
A kenning is a figurative expression that replaces a name or a noun. Often it is a compound of two words and the words are hyphenated. Kennings are usually associated with Old Norse, Icelandic, and Anglo Saxon poetry.
Modern Examples of Kennings:
- Ankle biter = a very young child
- Bean counter = a CPA or accountant
- Bookworm = someone who reads a lot
- Fender bender = slight car accident
- Four-eyes = someone who wears glasses