Seabiscuit wins the 1940 Santa Anita Handicap horse race in California

In 1939, Seabiscuit suffered an ankle injury and was retired to stud, becoming the sire of seven foals. At age seven, he made a comeback in 1940, competing against the top twelve horses at Santa Anita. Seabiscuit finally won the $100,000 purse he had previously missed twice.

What does the phrase 'What happened there is history' imply about Seabiscuit's performance?

What was the significance of the $100,000 purse that Seabiscuit won?