Those fabled dragon hoards in all the stories? Unsuspecting forest creatures’ lunch money.
(Actually some of the wyrms in this setting have the traditional penchant for hoarding, but it tends to be for magical things rather than plain old shiny objects.)

Do you recall where the Black Dragon’s been mentioned in the comic before? I think this is the first specific mention of the White Dragon, but you’ve seen some White Dragon priests in an earlier chapter.