Bug in Google Docs or a scary feature?

Today (15.8.2012) I’ve created new document in Google Drive and wanted to share it with a colleague of mine. I typed his address and before I hit the ‘Finish’ button I noticed that his email address changed to his (I did not know) gmail account. I was not aware that he was using Google, and I never communicated with him via any Google service so this behaviour really surprised me. Anyone with the same experience? My colleague than confirmed that this updated email is really his, but it is still kinda strange. At least for me it feels strange… What do you think about this?