Without knowing where, in the timeline of events, that this 'attack' took place, this video is meaningless. If the IDF had already landed and started shooting people, then these passengers were justified in what they did. If not, they were still justified because they're civilians, and the IDF attacked them on open water.
Palestinians report IDF airstrikes on Islamic Jihad targets in southern Gaza Strip (Haaretz)
from the article: Video: Gaza flotilla activists attacking Israel Navy commandos