No, the life on earth was here to early for that. What they are suggesting is after life evolved on earth sometime in the next 3 billion years single celled organisms from another planet may have reached earth. Or in theory, life from earth could have seeded another planet, and then a different impact could have sent some of that life back after billion years or so. Granted, it's more likely some life from one of those seed planets could visit another of the seeded planets.
However, I suspect whatever made the trip is unlikely to be able to out compete anything native to a planet.
The Earth is only 4.5 billion years old and the Universe is 13.75 billion - doesn't that give rather a long time for a generation or two of stars to cook up the suitable elements for life and give it an opportunity to develop before the Solar System was formed?
[Reminds me of the ending of the novel "Heart of the Comet"]
First you need a galaxy to from. Then you need at least one generation of stars to live and die before plants can form. You then need to give those planets enough to to form and cool down before life can show up. That's the start of the window of opportunity for life to show up. However, life on earth is ~3.8 billion years at which time the window closes and such things become visitors vs seeders of life. And this is important, all this needs to take place outside of the center of the galaxy where things are a little to energetic for life to flourish.
Not to mention you need a lot of stars to die to have enough material to create a rocky planet. A single super nova is not enough because the material is ejected over such a large an area.
Now, having said all this means is you shrink the window the distance such things can travel. Earth could have been seeded by Mars no problem, but 1/2 the distance means 1/4th the stars. Ejecta just don't move vary fast so even with a 1 billion year window you need to be really close to earth to seed it. More importantly the window between when life could survive and when life showed up less than 1/10th as long as life has existed. So, if we where seeded then we have probably had many visitors after the fact which is what this guy was saying.
PS: Of course if life is common enough both could have happened and even ridiculously unlikely events can happen.
Carl H. Gibson wrote a paper (http://arxiv.org/abs/1109.1262v1) that could just possibly explain why DNA is almost universal. It reads a bit science-fictiony, but the essence is that DNA could have formed fairly early in the universe's life, when it was small, and spread along with the expansion of the universe itself.
