I have a command where I'm using the console this way:

if ($input->isInteractive() && !$this->io->confirm('Provide confirmation', false)) {
    // some stuff...
}

But when I execute the command with --quiet, the output is obviously not displayed but the process still waits for the user's response.
For this reason, I think the --quiet option (OutputInterface::VERBOSITY_QUIET) should set Input::$interactive as false.

OutputInterface::VERBOSITY_QUIET Do not output any messages -q or --quiet

Ref: http://symfony.com/doc/current/console/verbosity.html

If I don't misunderstood the intended behavior, I think it could be labeled as a bug.