Yes, it's easy to spot a bent hanger by the RD cage pointing in or out with respect to the wheel. You had no problem spotting it, though you didn't recognize it for what it is.

OTOH- this is a matter of degree, and the real question is whether it's possible to recognize a straight hanger with the naked eye. There's debate here on the forum, but I believe that a trained eye can do it, though the right tool makes for consistent results.

Once your hanger is straightend, and the RD correctly adjusted, you can spot the bent hanger by any change in how the RD shifts. If the RD trims inboard, becomes sluggish on upshifts, or will not shift to high, the most likely cause is a bent hanger.