[nexuist]

Can you prove neither of you Googled anything related? Surely either you or your office mate could have done further research later on, which would involve searching those chemicals online and browsing Web pages related to them?

Alternatively if someone near you overheard your conversation, and Googled it, then Google could link all of your locations together and conclude that you are all interested in the same thing. This is how Facebook has its creepy ability to indirectly predict what items you are interested in - usually someone near you searches for what you're talking about later on in the day, and it guesses that it's important to both of you.