No Man's Sky doesn't have a seamless world. It is separated between space and planets. The first clue is the incorrect size ratio of ships to planets when in space and when on planets. The second clue to this is the video, at 2:16 in the video[0], two ships most far away from the player( not the three close in front ) disappear into the planet's atmosphere, that is the line that separates the two worlds.

[0]: http://www.youtube.com/watch?v=nLtmEjqzg7M