When we went on SAR when my ship was ready duty, we weren't the only ones that responded.

EDIT: Closet boat is expected to render assistance. All boats in area are supposed to respond and offer aid if capable.

Boats of that size would have multiple radios over multiple bands and would be required to monitor the international emergency channel. The second radio is used for normal ship to ship communication and you would have asked for their channel before switching to it.