The linked article said: "The motor I used—a BP Hobbies’ A2826-4 with a 14 x 8 folding propeller and a 4-cell LiPo battery pack—is more than is needed for relaxed flying. A smaller power setup could be used, but I enjoy the straight-up climb capability at times."
People have different wants and needs for electric sailplanes, including how fast they want to go up and how fast they want to glide.
One thing to consider is that the glider apparently balances with the suggested gear. If you use much smaller motor and battery, you MIGHT need to add some weight that is doing nothing.
Picking an electric setup has its pitfalls, so it is advisable to study the matter in some depth - or use combinations that somebody else has already proven to work well.