They are right. As the only post season games back then were the World Series, the 3 game tie breaker was needed to decide the final regular season standings. And to determine which National League team would play in the World Series. So therefore they were not post season games, but regular season games.

Final Standings 1962
https://www.baseball-reference.com/leagues/majors/1962.shtml

The Giants & Dodgers also had a 3 game tie breaker series in 1951.
Final Standings 1951
https://www.baseball-reference.com/leagues/majors/1951.shtml

Have to disagree because the regular season was in fact over.

Those games were not scheduled and have to be considered post season.

Just my $.02

Some consider those games the last real play offs.

1951
How many times did the announcer say "The Giants win the pennant"?

:)

The regular season may be over, but statistically the tie breakers count as regular season games and determined the pennant winners prior to 1969, when mlb started using divisions. They still count as part of the regular season today.

https://en.wikipedia.org/wiki/List_of_Major_League_Baseball_tie-breakers#:~:text=As%20these%20tie%2Dbreaker%20games,to%20as%20%22Game%20163%22.