I don't think the scoring rate of the league in itself tells us much at all, stats are meaningless without some sort of interpretive context. The (mostly implied) context in this case seems to suggest the earlier fifties were lower scoring than the later fifties and sixties because it was harder to score, I don't know if I buy that.
There seems to be a clear correlation between league GPG and the # of high end scorers:
In 47/48 -
LEAGUE GPG- 2.93, there were 17 players (min. 40 games) that were 0.70 PPG or better and 12 players at 0.80 or better
In 48/49 -
LEAGUE GPG- 2.72, there were 16 players (min. 40 games) that were 0.70 PPG or better and 7 players at 0.80 or better
In 49/50 -
LEAGUE GPG- 2.73, there were 14 and 9 players
In 50/51 -
LEAGUE GPG- 2.71, there were 15 and 8 players
In 51/52 -
LEAGUE GPG- 2.60, there were 16 and 8 players
COMMENT: League scoring and scoring levels of the elite scorers seems to be on a downward trend after reaching unprecented levels during the war years. There is lots of U25s in the Top 10 scoring from '48 to '50.
In 52/53 -
LEAGUE GPG- 2.40, there were 9 and 6 players
In 53/54 -
LEAGUE GPG- 2.40, there were 9 and 4 players
COMMENT: League scoring and scoring levels of the elite scorers continue on a downward trend. Most of the elite scorers from '51 to '52 who are in their prime, see drops in their PPGs (Kennedy, Sloan, Gardiner, S. Smith). There isn't any particular statistical anomoly that explains the drop in league GPG. The Red Wings, and Howe, are not affected in 52/53 as they score as many goals as they did the year before. The Rangers and Habs score a lot less goals in 52/53.
In 54/55 -
LEAGUE GPG- 2.52, there were 15 and 7 players
In 55/56 -
LEAGUE GPG- 2.53, there were 16 and 8 players
In 56/57 -
LEAGUE GPG- 2.69, there were 16 and 13 players
In 57/58 -
LEAGUE GPG- 2.80, there were 21 and 13 players
In 58/59 -
LEAGUE GPG- 2.90, there were 28 and 18 players
COMMENT: League scoring and scoring levels of the elite scorers goes up. There isn't any particular statistical anomoly that explains the rise in league GPG.