Composting fail?

A few months ago I got really into the idea of planting and growing some fruit or veggies on my own. I tried to quickly learn about all the tips and tricks and decided to start a compost pile. But before I could actually do that, got quite sick and was out of commission for a few weeks. I'd only collected some dried leaves, branches, old cardboard stuff and kitchen scraps and put it in a cardboard box as I hadn't bought a bin at that point. Lo and behold, when I got back to it a few days later, there was a mango plant growing out of the cardboard box 😂. It's been a bit more than a month since then and I finally decided to put it in a pot since it's healthier and stronger than any other thing I've intentionally planted. Don't know if I should characerize it as a compost fail or a gardening success 😂