Nor is the discussion regarding the languages only. It is about the additional set of tools that one uses in order to build a web application in those respective language. Consider the phrases "and its associated frameworks" and "similarities between Rails and Django given the structural similarities between Ruby and Python" as clues that this is not about the languages per se. Or from the previously written essay, "the construction of a Ruby on Rails app ... that makes use of Devise for user authentication, RSpec for unit testing and Cucumber for behavior testing."
The author therefore quite clearly "recognize[s] the parallel between installing several gems and installing several packages" and is instead focusing on a specific aspect of that parallelism; inter-depenency.
Ruby makes heavy use of gems, which appear to be like more complex Python libraries. I say "more complex" because they appear to bolt onto each other far more heavily than Python libraries. If I want to make a complex application run, chances are I'll need five gems to do it... and versioning is extremely important.
The point is that the interconnections between Ruby gems appears to be much stronger than between Python libraries, and I interpret the above to mean that version mismatches occur noticeably more frequently in Ruby than in Python.