An "ERO" only occurs on you first turn at the table and all 15 balls on the table.
Therefore, if you break and run all the way out, it counts.
If your opponenet breaks dry and you run all the way out, that also counts.
^^ This ^^
Only thing I'd add is that if I break dry, you miss your first shot, I miss a shot, you miss a shot, etc, etc (no group has been claimed yet), and then I claim a group and run out in the same inning, it's an ERO.
Also, if I break dry, you make four or five of one group, miss, then I get out (making all seven of mine and the 8) in one inning, it's an ERO as well.
All leagues are different, YMMV...