"It’s also worth pointing out that we do take certain technical measures to limit the data we collect. We’ve designed Persona so that the identity provider – including the fallback Identity Provider that we run – does not learn your browsing history."
That does not say "we only store your email address". It also does not say they are storing more than that, either. In any case, the data is not encrypted, so my argument stands.
"Many sign-in systems carry your profile data with them; some even share that info with other sites and social networks. We believe you should control how your personal information is shared. Persona lets you get started with just your email address; you can add your profile data later, when and where you think it’s appropriate."
Whatever that "profile data" is, can be requested by the government.
The "profile data" that refers to is the profile data you want to add per-site. It's got nothing to do with Persona.
All Persona knows is your email, a password and the fact that you (maybe) want to authenticate at some point (but it doesn't know where, and it can't be sure you're actually trying to authenticate somewhere even).
That does not say "we only store your email address". It also does not say they are storing more than that, either. In any case, the data is not encrypted, so my argument stands.