I think they're talking about just what device they have and OS version (but that's available in the user-agent anyways[0]), since that tells an adversary what exploits to purchase or put resources into developing. Who knows, maybe 30% of congress people haven't yet upgraded to an iPhone with the A12/A13 chip (which can't be exploited via the checkm8 exploit).
0: https://developers.whatismybrowser.com/useragents/explore/so...