I have trouble understanding how Yahoo's moves are GDPR-compliant : if just one European citizen was part of the group to be archived, at least some if not all

I have trouble understanding how Yahoo's moves are GDPR-compliant : if just one European citizen was part of the group to be archived, at least some if not all data in the group can be considered part of their personal data (as they were either sender or recipient of messages) and therefore there should be a mechanism allowing them to download that data. Am I getting it wrong ?