i am almost sure it was becuase of long term storage with some fuel inside.
Best to keep tank full and add stabilizer to it before you put the bike in storage. Also make sure you add stabilizer on your last ride home to ensure stabilizer gets into carburettor and stuff too.
Easier, safer and more reliable.
Worst you can do is to leave the tank half full with gas.
And fully draining the tank+carburettor is also much hassle.
So you are suggesting to add another fuel filter? as GS already has one.