There are two different ways “handicap” usually gets used in horse racing. One is to refer to the process of calculating which horse is likely to win, and how to profit from that intuition (also known as “being good at betting on horses”). The other is a system in which horses that have proven to be faster than the rest of the field carry extra weight in a race.
Today, though, we’re using it to refer to a horse that recently raced in Tokyo, who’s ridiculously fast but seemed to do everything he could to let his opponents pass him for the win.