By mining I assume you mean “meaning”? If so, the kind number is just a number that is set on every event to “categorize” it.

For example, an event with kind = 1 means that this event is a “Text” event and an event with kind = 4 means that the event is a direct message. This let’s clients process these events in a specific way based on how it’s defined in the protocol.

You can see a list of the current “standard” event kinds here: https://github.com/nostr-protocol/nips/#event-kinds.

Why do I make this public?

This data is not secret in any way. I share it because I love statistics and data.