Given a block_id, what would be the most reliable method to decide if the block was generated by Views?
As Clive said, each block will contain the module name from which it was created in the block configuration. For views blocks, it's views module.

This module information will be available in the form structure itself, like below:

$form['module']['#value']


So you don't need to query the database to retrieve it.

Pseudo code:

function my_module_form_block_admin_configure_alter(&amp;$form, &amp;$form_state) {
  if ($form['module']['#value'] == 'views') {
    // ...
  }
}