League scoring took an especially unusual dip in those two years after scoring levels seemed to have returned some consistency in '48/49. It was 2.60 in '51/'52 then was 2.40 for the next two years before rising in the late '50s. .
Was there anything unusual that would have lead to this drop?
Yes, I've studied this subject quite a bit and there is a clear explanation. But you should look at a broader period, not only those two seasons.
The first thing to keep in mind, is that scoring can decrease for multiple reasons. It doesn't necessarily mean the league is stronger or weaker. Remember that scoring is the difference between offense and defense, always a result of interplay between the two. So, scoring can decrease, in general, because of better defense or weaker offense.
In those seasons, the main reason scoring is lower is the latter - weaker offense (weaker scoring forwards). It's kind of a transition period from the M. Richard, Abel, Bentley, Lach, Schmidt generation (which was pretty decent, not great) to the Beliveau, Geoffrion, Moore, Bathgate, Delvecchio generation (which was stronger and deeper, and includes Howe as well).
Between Rocket and Beliveau (who are a decade apart in age), the scoring forwards are exceptionally weak, in comparison. And these are the guys who are at their bests around those 2 seasons. In that 10-year period, there's Howe and Lindsay (who's not that great), and that's about it. Also Kennedy and Olmstead (the best of the rest), but they weren't great scorers. No depth of talent.
Guys like Schmidt, Abel, Bentley, Lach were on there last legs; and It was just before Beliveau, Moore, Bathgate, Delvecchio.
There weren't goals being scored mainly because there were few good offensive forwards in their primes.
This is the same general reason why Howe was so dominant in scoring during his four consecutive scoring titles - very weak competition.