Let me begin with that this idea is fresh to me and rough around the edges. With that being said , it kinda makes sense . Here are my thoughts , if I were an advanced civilization and let’s say something happened like our whole race was hit with an incurable disease . And their solution was to let Mother Earth and natural selection solve it for them . They froze themselves and had a Ai system in place to defrost them when it met their criteria. But we unfroze them unknowingly , through our warming of the planet. And all the craft we see is trying to get sense of what the earth is like now . They may well be millions of years old .