It would be quite unusual to get 5-6 meter waves at BF4. That's more of a BF8 level. I bet it's misreported. Most ships, even small ones, will not care for BF4.
Couldn’t the waves originate elsewhere where it’s BF8? What’s going to stop a wave in the open ocean?
Waves can travel, but big waves quickly spend their energy, because, unlike swells, they break. When the wind goes down, waves quiet down very quickly.