Why did my SO rep just jump by 100?
My Stack Overflow account reputation increased from 196 to 300.
How did it happen?
Check your reputation audit.
It looks like your SO account just went over 200 points, so your associated account bonus (100 points) probably kicked in.
You get 100 reputation when associating accounts - did you by any chance only now associated your Meta account with your SO account?
This reputation boost is not visible anywhere as far as I could see, so I can't really be sure this explain your case.