One of the first tests for infringement is "substantial similarity"(see [1] for example). If you claim copyright infringement on the basis of any small number of characters your case will be tossed by the judge. There isn't a specific number of characters that need to be copied before it becomes "substantial" because the court gets to rule on that based on the context etc.
The realm of what does and doesn't constitute a license violation is complex and, in the end, up to the whims of the legal system. For this particular issue it appears that an actionable amount of the project is in use.
