Look pal, I've given you all the information you need. It's really all right there. I can lead you to data, but I can't make you think.

If you want to go on believing that someone at Signal has found a way to backup your contacts so that you can recover them when you use a new device that does not in any way involve Signal collecting your contacts and storing that data to push back down to you later be my guest. You believe in magic, and I'll continue to believe their own statements, code, and documentation.