MySQL hidden files on ubuntu taking up space
looks like this command worked for temporary solution:
PURGE BINARY LOGS BEFORE '2019-10-19 22:46:26'; #your date

(mysql manual)
Still working on the long term solution. Per mysql manual - these were the logs of select statements (which are typically huge in my case). Not 100% yet on whether I need these :) In either case, thank you everyone for helping troubleshoot. This was blowing my mind for a bit, but all it took was browsing into the folder itself, and seeing hundreds of huge files!