It's possible it spread from seed, although I've never seen that happen in my garden. It's usually more likely that it will crawl out of a pot and attach right to the ground. Whether you pull it or not is up to you. It's a non-native invasive species, but smells really nice when mowed. If you decide to yank it, don't wait a minute longer!

Mint non-invasive?!?!? It's an absolute THUG!

10 feet away? - it's only a short distance for mint to travel. A ledge? - just something to travel down with the greatest of ease. There are many threads here on the subject, which I recommend you read. Start digging it up now, unless you plan on an all-mint garden!

I thought she said it was a non-Native invasive plant, not a non-invasive plant.

She did. Apologies! But non-natives can be worse thugs than natives, you know!

HAH! I just found mint growing on the other side of a deep-bedded retaining wall. The THUGS have somehow gone under the footings and set up shop. Un-friggen-believable!