In this situation we are not so much concerned about the weight of the people on the seesaw but their position. It can be seen that the person on the left-hand side has moved out a way from the centre or fulcrum. Obviously this would cause the seesaw to tip over to the left assuming the two people on the seesaw where the same weight as each other.
In the case of the forklift the forks have not been entered for the into the load resulting in a gap between the forks and the load. This is known as undercutting in the trade and whilst it is practiced by experienced operators in difficult circumstances it can lead to serious forward instability of the forklift.