That random stranger saved my climb in Austin

Last spring I got a call to prune a big live oak near Zilker Park. The homeowner swore the tree was fine, just wanted a light trim. I was about to climb when this old guy in a beat up bucket truck pulled over and yelled out his window, 'You ain't checking that collar first, are you?' I ignored him at first, but he kept hollering until I looked closer. There was a huge crack hidden behind the ivy, right at the main union, big enough to put my fist in. If I'd put weight on that limb with my saw, it would've come down on my ropes. I thanked him and he said he'd seen two climbers killed the same way in the 90s. Now I always strip back the bark and ivy before I even tie in on any oak. Has anyone else had a random stranger on site save them from something dumb?