The paper^[1] discusses metagenomic information that suggests the results are not the subject of contamination:

> As only one pair of reads was found in the metagenome, the analyzed fragment was covered just once, necessarily capturing one gene variant. These results strongly suggest that the isolate originated from the permafrost layer and not sample contamination

1. https://www.cell.com/current-biology/fulltext/S0960-9822(21)...