That's why if I'm not mistaken, the all time high could be a average of what other exchange had during that time.
Yes. Sites like Coingecko or Coinmarketcap can be used to check the average price from the listed exchanges on the sites. Although, I only use the price that I saw on the exchanges that I am using without doing the average because the prices will almost be similar. The all-time high is $73750 on Coinmarketcap.