Although informal, this is a much closer definition of epigenetic than the OP
No, its not
relating to, being, or involving a modification in gene expression that is independent of the DNA sequence of a gene
The human DNA is set to hetero as the default. This latest theory debunks the notion that it is genetic. Too many identical twins have varying sex habits, and gay would eventually evolve itself out if it was passed due only to genetics. So the result of being gay is the expression of that gene from its default due to external modifications from the parent.
Obesity is the perfect example of epigenetics. A trait that is passed due to behavior of the parent.
This study means being gay is a choice. The epigenetic trait is passed on, but external modification can effect your behavior. Much like obesity is passed on due to the amount of sugar that is now available in our diet. The Swedish famine study also confirms that diet choices by parents effect offspring, but is not genetic.
So you can choose to remain gay, because your ancestor somehow modified that default gene; or you can choose to modify that epigenetic factor.
Either way, its external forces at work. It boils down to a choice someone made at some point in your lineage.