You unlocked all the content in Fight Lab.
The "content" that is referred to by the achievement is actually all the moves you can purchase for Combot using the points you gain in Fight Lab. From the Fight Lab menu select "Combot Tuning" and you should see eight bars with percentages on them. When you unlock a move for Combot the moves end up here waiting to be purchased with your points. Once each of them is at 100% the achievement will pop. It will however take around 3 million in points to make this happen. If you are good at the Stage 5 boss you can get 100,000 points every two tries.

The percentage bars that say "Stage #" at the bottom of the eight bars you need to fill for the achievement have no bearing on this achievement so ignore them if you want.

DarkSephiroth has a rather interesting way of gathering points and money here.