DOING A FLY BY ON EARTH WHILE SEEDING OTHER PLANETS

Look, we see an engineer drink a cup of this goo and it supposedly leads to all sorts of growth on this planet whatever it is. Now, go to the ship scheduled to go to earth and its cargo bay full of thousands of containers. Couldnt be that they were schduling a check up on earth and between here and wherever, they were going to seed more planets? It doenst take but a small amount to do a planet...remember? Where is all the they are going to kill us coming from?