The app was intentionally subtle, in that it had no application icon, which would presumably make it very difficult for user to disable contract tracing if they had enabled it. If you managed to uninstall the app, it would get reinstalled silently again.
2. The lawsuit alleges that there was no legal requirement or court order. Even if there had been, the lawsuit argues that the conduct would still have violated federal and state law and constitutions.
It is really pretty shitty, and, IANAL, probably is/was illegal, with the caveats that (a) I'm not sure whether Massachusetts or Google or both should be considered responsible; and (b) they might try to argue that a user's acceptance of Google's ToS and privacy policy constitutes permission.