The company's history page says they were part of the merger in 1967 that created "Big Nokia": https://company.nokiantyres.com/about-us/history/#:~:text=19...
This changed in 1988 with the formation of an LLC, in 1995 they went public and in 2003 shares still held by the parent company were sold off to Bridgestone.
Nokia did manufacture rubber boots though, before they spun off the footwear division in 1990 and went all in on electronics.