How battlemetrics read data from server?
Where they got my entity count, map size and last wipe time?
How to restrict access to read that info?

If someone know how to hide some information at Battlemetrics, i'm willing to pay for it 10$ paypal as friends and family.

I suspect that Battlemetrics uses the Steam API to collect this data.  The only way to prevent Battlemetrics from collecting this data would be to stop listing your server on the server list, which is also managed by the Steam API.

There have to be another way, because i was playing with map files and i managed to make it show: Unknown
But with corrupted file, now it seems not working anymore.

There is a way (pretty easy) to remove the specified info but not sure how long would you last on the server list with the informations hidden