In this instance, it’s stating that the channel_type changed from 9 to 10, which means it went from a Public Group Channel to a Public Super Group Channel.
I agree that this data is not provided in our docs and I will work with our team to try and make this a bit more comprehensive. I would say that you should not expect the new/old values to be a string or an int as there are scenarios where it could be either depending on the key.