horse racing riddle, page-43

Theo, If I follow you correctly I think there is a mistake.

So race all horses in 5 heats and then race the winners of the heats in race 6.

Now we will say heat 1 was the race where the winner of race 6 first raced. Heat 2 the race where the 2nd fastest horse of race 6 first raced and so on.

Your 7th race is the three winners of race 6 and the 2nd and 3rd of heat 1.

How do you know the 2nd place of heat 2 is slower than 2nd or 3rd place of heat 1?