What Google could be doing is remote logging on the laptops - logs uploaded to ze cloud every time you connect to the mothership. Plugging in USB drive leaves trace with USB ID, volume information etc. Windows also logs this and more http://www.forensicswiki.org/wiki/USB_History_Viewing
Protip: to exfiltrate data with minimal trace your best bet is taking out the drive and reading it in another computer (using write blocker for best effect), this can still be traced if someone is logging SMART written/read data (I am, but Im paranoid), not all HDD/SSD vendors provide this info. Second best is booting from USB drive so the original OS never sees the plug/unplug event in the first place, I have no idea about current state of UEFI/AMT logging going on tho.
Disclaimer: I used to do forensics.