Not only was there an above average number of HRs in the game, there was a slightly above average number of walks and strikeouts.
There were 9 walks in 10 IP. The MLB average per team is 3.3 per 9 IP. So that would be 6.6 for two teams. 9 in 10 is above average.
There were 25 strikeouts in the game or 12.5 per team. The MLB average per 9 IP is 8.5.
Half of the hits were HRs. 10 out of 20.
The average team gets 7.3 non-HR hits per game. So you would expect 14.6 in 9 innings. But in 10 innings there were only 10.
Maybe most all-star games are like this. But this game did shatter the HR record.