There appears to be a lot of imagination in this article and little in the way of observable, verifiable evidence. The UM focuses on what are called Fundamental Questions or FQ’s. Some of which for this article come to mind.
Why do they define cosmic dust particles as having minerals that make them magnetic?
How can those magnetic dust particles survive a 12km per second entry into the Earth’s atmosphere and the resultant heat that they acknowledge would accompany it, and maintain their magnetic properties when its been shown that magnetism is destroyed at temperatures that would melt rock or dust particles?
How do they know the makeup of the cosmic dust that fell on the Earth during medievel times?
There is something that is observable from the article. The fact that there are particles about .01mm in diameter that are magnetic and found in rain gutters in Europe. That is observable evidence. However, you are correct. How it got there was not observed. I wonder if the researchers even thought of the FQs you asked in your post.
Great article! Now I want to go and dig through the sediment in the rain gutter I put up on my back patio. Now where’s my magnet?