That's not enough if you are using an online crypto wallet. You also need to check if the seeding is deterministic. And also it could send the data 'later' when

That's not enough if you are using an online crypto wallet. You also need to check if the seeding is deterministic. And also it could send the data 'later' when you next visit the site rather than now, storing it in indexeddb/localstorage/ etc. So you have a false sense of security. Also as in this example loading a .jpg could be a way of communicating something.