Hi. Welcome.
There are all sorts of reasons it doesn’t always match up, the way card transactions are processed can vary and if Monzo doesn’t have the data for each variation, it doesn’t know and just guesses.
If you scroll to the bottom of the transaction in grey it will give you the ID of the transaction, hopefully it will say Etsy in it somewhere.
You can also report it to Monzo to have it corrected, but I wouldn’t hold out much hope of it being quick (or at all in some cases), you can see more about this here…