Just for information it seem that only the installer from their website first download page[0] is bundled (it has "bundled" in the name). When in the same page there is a link that says "Show additional download options"[1], in that page you have access to "clean" installers.

The way they did it is quite shady.

[0]: https://filezilla-project.org/download.php?type=client [1]: https://filezilla-project.org/download.php?show_all=1