It says when friendly ships blow up within the radius it gains a percentage of their health. However, it also states that there is a bonus if the ship was boarded when it blows up? I think I have witnessed them gain health from the destruction of enemy ships, too. I havn't really tested it though, so it could be wrong.
So either the discription is wrong, or it's just not very clear. Does it mean ships that you have taken over by boarding?
Also, is the boarding ability is confusing too. Does the enemy ship have to be killed by boarding, or can it be killed by something else while it's being boarded?