It's awful that you had a bad experience, but no. Nowhere near 70% of hospital deaths are from preventable mistakes.
I would also note that in your experience, you ended up trusting a different doctor (ophthalmologist), not ChatGPT. Second opinions from other qualified professionals is a thumbs up from me.
Just like I wouldn't go to my podiatrist to treat a complex case of rosecea, urgent care and GCP aren't for specialized, complex and rare cases.
I generally expect such counts to be under-representative. I'm also probably conflating cases of "this person was going to die regardless but the hospital screwed something up" with "this person was not going to die but did die because the hospital screwed up." It's not clear how any source would avoid that conflation though.