I wish this article shared more about how this tomb was discovered. Was it buried under mountain of dirt? Under a jungle canopy no one explored? Has it been there all along at an existing ruins site but was hidden in some way? Give us details man!
These site inventories are generally filled using cultural resource management records submitted by surveyors, miners, construction companies, etc. who are often legally required to file them. A few tour guides I’ve used in Mexico found new ruins in the jungle and submitted their records with GOS coordinates and pictures. If locals knew about it, someone likely recorded the location a while ago.