Some cases are. Some evidently are genetic.
No-they are not-there is no documented, provable scientific evidence of homosexual tendencies being genetic/inherited. As a case manager, I’ve had homosexual/lesbian clients-as well as acquaintances and a couple of relatives who were gay or bi. Every one of those people recalled an older relative or friend inappropriately touching/initiating sexual contact with them-usually at around/slightly before the age of puberty-about 9 to 12 or so. Male children who were sexually abused were sometimes feminized by a possessive mother who also trusted sketchy relatives/friends alone with her kid.
If they were ashamed/scared to tell anyone, the sexual abuse continued, and the pattern was set. If they told a parent, or someone who told a parent, and went to a therapist, the issue was treated like the childhood trauma that it is and the kid can develop heterosexual desires like nature intended...
That is just my experience and my dos centavos-you are entitled to any opinion you choose...