When you see the "chunks" of ice floating after he got out, it gives you a better understanding of when someone says "rotted ice"
The ice can look good, be quite thick, and yet be as dangerous as a skim coat in November.
When ice forms, it generally forms in horizontal layers, but when it "rots" it breaks down vertically. Think of which direction air bubbles will head?
My theory is simple: "When the ice turns grey it's time to stay away!"
I fish late season ice that was a day or two from doing the same thing (years ago). I had to plank out to the more "solid" ice, and was fishing on 7-8" of what was probably frozen slush at some point. I could scuff my feet through 3 inches with little effort. I was fortunate that nothing bad happened, but at that point I considered the season over for me. I refuse, to this day, to push the boundaries of safety just to catch a fish.
I'm glad you got out safely and with minimal loss of gear.
Did you try to retrieve it later that year?