No? Lets say we intro-/extroversion is either heritable (with prob .5) or random(with prob .5). If both of your parents are introverted you have a 50% chance of inheriting the introversion of your parents or a 50% chance at a coinflip, which gives us 75% for introversion and 25% for extraversion.

I'd rather interpret it as "50% are fixed (nature) and the other 50% are a coin flip (nurture).

No:

https://en.wikipedia.org/wiki/Heritability

No, because it's not a binary choice. There are degrees to which people are open to new experiences or extraverted.

I took it to mean a covariance of 0.5.