A gross, high-level summary would be that jDownloader automates "interesting" data file extraction and retention from the World Wide Web. In essence, a file ripper from websites. But it automates a lot of the "nonsense" you have to go through (click-thru this, wait for that timer, etc., etc.). It's this automation that makes this advantageous over wget, for example.
But, there are TONS of websites that all work slightly differently. So there are literally hundreds or thousands of modules customized for a slew of different websites.
Almost certainly this offending code is in one of these specific modules. The article/summary states "3rd party". It might be more appropriate to think of it is as User-Community provided. The main developers maintain the base code and a host of players are creating/adding the modules.