Barbarians Spawning from Ships/Nothing?

I noticed a few minutes ago that a Barbarian unit spawned right outside my borders, but there was no encampment nearby, and my units had visibility of all of the land tiles nearby. Also, I had another barbarian unit spawn on that same tile about 10 turns earlier when it was out of my line of sight. However, my units were able to see the tiles connecting to it, so it couldn't have walked over from another part of the map. They also can't be rebels, as my empire's happiness is at +13.
Although, something I did notice is that when the second barbarian spawned, there was a barbarian galley in the water on the next tile. So, is this a glitch or have they allowed barbarian land units to spawn from their boats?

A screenshot of the second barbarian spawn is attached.

Barbarian also spawn if they plunder a trade unit.

The honor opener will notify of new barbarian encampments appearing.

barbarians will spawn (multiply when they plunder a traderoute) .. Surprised the hell out of me first...

Moral of the story protect the trade route units from barbarians ...

They're rather Pirates than barbarians