This is not true, this is Donald Duck history, Gustav Vasa was the first in this family being king. Krister Vasa, was NOT king of Sweden 1435, that year the Swedish throne was vacant,
Eric of Pomerania (1381 or 1382 – 24 September 1459) was the ruler of the Kalmar Union from 1396 until 1439, succeeding his grandaunt, Queen Margaret I. The Engelbrekt rebellion (1434–1436) was led by Swedish nobleman Engelbrekt Engelbrektsson (c. 1390 – 4 May 1436). The Swedes had been affected by the war with the Hanseatic League (1426–35) which affected trade and disturbed Swedish exports with Schleswig, Holstein, Mecklenburg, and Pomerania. The rebellion caused erosion within the unity of the Kalmar Union, leading to the temporary expulsion of Danish forces from Sweden. https://en.wikipedia.org/wiki/Eric_of_Pomerania