IMO you most likely hit the shoulder and got 5" of penetration into a single lung, when the bull took the first step the shoulder bone sliding across the ribs under it would break off the arrow where they meet. I've made the same shot at 20 yards on a mature bull and ended up not recovering him. I held tight to the shoulder and the bull ran about 50 yards after the shot and stopped and started coughing, I thought he was dead so I backed out and came back with my wife and kids a couple of hours later to recover him. There was a small golf ball-sized chuck of lung blood where he stood and he just walked out of there. Looked for the rest of the season for that bull and even took hounds to try to turn his carcass up a few days later. I'm pretty sure I have a picture of a trail cam of him a couple of years later.
Who knows about your follow-up shot, if it was high you may have just poked it through his back strap like a shishkabob.
As far as your setup, I personally don't like outserts but feel like they were not the issue at all, I'm shooting a 500gr arrow at 278fps with a mechanical and was able to push one through 4 ribs of a bull at 60 yards this fall.
Honestly I feel like this shot was more forward than I’m comfortable with. He lived long enough to run 115 yards and tip over next to my hunting partner.
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