The question should be - does Google keep a profile on you based on the content of your emails?
I'm pretty sure they are able to serve ads without keeping a profile, making the decision solely on the content of the email being read. However, that may not be the case.
He's clearly talking about humans reading your mail. No email provider has humans reading your mail for purposes of spam detection, at least not in the usual case.
The question is perfectly valid: seeing that other companies have clear policies on the extent to which employees can access your data, how come Google doesn't have any such policies?
Not sure what kind of profile this ends up being, but it can be quite entertaining when I get ads about sumo wrestling (because of previous emails from appsumo)...