Why was the experimental MiG 1.44 so similar to the experimental TKF-90?
I once led a group of Antonov engineers through the aircraft exhibition of the Deutsches Museum in Unterschleissheim near Munich. There are two halls connected by a walkway, and from that walkway you can see the restoration workshop which is located between those halls.

When the group had long left the walkway, one engineer still stood in the middle of it and gazed down at the Dornier Do-31 which at that time stood in the shop for cleaning and repairs after many years in the open. I walked back (with one of our interpreters) and asked him what fascinated him. He said to me that this was the first time he saw this aircraft in person. And he continued that he knows every rivet in it. He had studied it in the early Seventies for several years when Antonov was tasked with developing a VTOL transport aircraft. In the end, they abandoned the idea (like NATO did a few years earlier), but this airplane had been the center of a part of his life.

Don't think bad of this - it is just good engineering practice to study what others have done. If you want to develop something, look what others have done before you and try not to repeat their mistakes. You might as well marvel at the similarities between an F-15 and a Su-27, a Concorde and a Tu-144, or a Space Shuttle and a Buran. In the end, they were designs made for the same purpose, and it is no wonder that they turned out alike. It just means the engineers did their job properly.

In nature this is called convergent evolution.