Were the aliens actually planning this ?

When all the people are boarding the ferry, you can see 3 tripods on top of the hill, which clearly can see all the crowd.
First time I saw the movie I was wondering why they didn't attack like at the beginning. I thought the director made this tense scene strictly for dramatic purposes.
When I rewatched, it seemed the aliens were intentionally herding as much people as possible onboard the ferry so they can be easily picked up later by the one hiding in the water.
Anyone saw any director's commentary or something that clarifies this ?