Imagine the brown cube is the base.
If the two adjacent faces folded upwards the rest of the faces would have to wrap around the figure.
At least one face will overlap another, and there will be one missing face to complete the figure.
Visualize this net folding. Sketching this net onto a piece of paper and cutting it out may prove to be helpful in solving this problem.
You should be able to conclude that this net, in fact, does form a prism.
At first glance this net may seem to form a prism, but count how many faces there would be.
This net will not form a prism because there are 7, instead of 6, faces. This means that two faces will overlap.
Try and visualize this net folding. Are there any tools that can help you solve this?