He said “it was possible”:
You might want to read about the backstory of that clip and how it was edited and cut to make it seem as if Dawkins actually believes, or even only considers it a real possibility, that aliens engineered life on earth.
In reality,
he was asked to bend over backwards and
assume that life on this planet had no natural origins but instead was designed, and try to come up with a hypothetical scenario in wich such was the case.
He responded by saying that
in that case, perhaps aliens bio-engineered life here, and subsequently added that
those aliens themselves would then have had to come about in some darwinian way on their home planet.
It's actually a prime example of creationist "honesty".
Not only was Dawkins' answer dishonestly edited and cut to make it seem as if he actually believes any of that, he was also flat out lied to concerning the purpose of the interview.
He was told it was for an educational science program for students, while in reality it was a creationist propaganda flick. Had Dawkins known what the purpose of the video was, he would have NEVER agreed to the interview. Or at the very least, he would not have entertained those silly hypotheticals and would have made sure that they wouldn't have been able to engage in such dishonest editing.
It should tell you something that your creationist heroes feel the need to resort to this kind of disrespectfull dishonesty.