That is what they hope to find but nothing indicates any of this exists. In regards the different metal compositions. That is to be expected as no star/solar system has the same proportions as each develops from gas clouds with different rates of heaver atoms due to the number and frequency of supernova to have occurred previously within the local space.

We have been finding metros on earth that originated from Mars for decades, you do not need intelligent life for it to happen.

The astrophysicist seems to be pushing this angle to sell his books.

I would love for them to prove the existence of what they are looking for (I am studying an MA in astrophysics) but while extra-solar source is incredibly interesting, nothing they have found so far is any indication of anything in regards extra-solar system life.