Not really, no. Shyness is more akin to anxiety, and not engaging in conversations doesn’t automatically mean it’s an anxious behavior.
Introverts aren’t the way they are because they’re shy or have anxiety about participating in social situations. That’s just social anxiety, and introversion and social anxiety are not mutually inclusive.
This person really just seems like they’re fairly in the middle of the introvert/extravert spectrum.
I just stopped talking to those relatives.