Hey knackers , if its what i think it is , then its a good thing , if not then i dunno.
In growing , there are a few methods of making the plant grow in different direstions
By manipulating the stem , either by bending ( low stress training ) or by actually crushing the stem ( supercropping ) it seems unnatural or brutal , but the hormones in the plant heal the broken fibers and the plantt turns into superman
Usually its left with a knot or ball like a big knuckle when it heals
So in your case maybe you accidently bent or injured the sten and thats its repair job , maybe you have a cat , who chewed it up and its repaired itself ?
Or it could be a fungus , in that case wait to see if it spreads , then make a decision ....
Also, wait for another opinion....