I don't know this particular story, but — FWIW — it's common for different teams working in the same field to be aware of each other's manuscripts and impending submissions. When two teams are about to submit papers with the same discovery, they'll often work with an editor to put it in the same journal issue.

By coordinating a simultaneous publication they can get extra publicity for the discovery, both get the first-mover advantage in citations (both papers get cited by everyone), and also get breathing room to be fully rigorous and write the best possible paper.