the "i don't have a choice" thing began as a legal defence in certain backwards areas of the deep south (i think it was an area of texas) that were enforcing sodomy laws. the judge allowed the defence, the person avoided a sentence and it's become this thing ever since.
a large amount of biologists will tell you something like "homosexuality is probably genetic". what that actually means is "there may not be direct evidence of a genetic cause but, if it's not genetic, then i don't understand it. genetic is therefore my best guess.".
every little once in a while you'll see some headline that claims they found the gay gene, but the research is never solid. it tends to actually usually cycle around hormones, which probably does have a genetic basis, as it's something that's physiological. but finding a genetic cause for less masculine behaviour in cis-men (and less feminine behaviour in cis-women) has absolutely nothing to do with sexual orientation. those hormonal reactions may place people into social niches, and that may have something to do with it, but it's not direct - it does nothing to explain the gay jock or the femme lesbian. worse, these studies are often inapplicable to women altogether.
it's entirely possible that it is neither genetic nor a conscious choice.
by analogy, consider somebody that is very shy. that shyness is not genetic, it's a reaction to various life experiences - something traumatic, over parenting, social isolation and etc. but the shy person generally does not choose to be shy, it becomes deeply embedded within their nature. further, a shy person can overcome their shyness - if they want to, which some shy people might not.
i have a bit of an unusual anecdote that i usually avoid when i have this discussion. i'm transgendered - born a male and transitioned to being female. now, orientation and gender aren't the same thing. in fact, statistically speaking, most male-to-female transgendered people are attracted to people that define themselves effeminately, and often to cis-women. when i was first going through treatment, i was asked questions about orientation and while the truth was that i wasn't really interested in either gender, i did find myself more attracted to women. i had a lot of questions about how i was going to react to both men and women as a result of hormonal changes, so i decided to experiment with some pornography to try and determine if i had any real attraction to men - or if i would develop one over time. what i noticed was that, the more gay porn i watched, the more i responded to it - and i realized at that point how fluid orientation is.
now, i'm not suggesting this kid was brainwashed with gay porn, but there are other social cues that could lead somebody to homosexuality as a culmination of experiences within their environment. it's such a complex thing with so many variables that it would be virtually impossible to test for - as a hypothesis, this is really not falsifiable. but, that doesn't mean that it's wrong, it just means it would be virtually impossible to demonstrate.
now, i'll be honest with you - i'd rather see society accept it as a choice. i want to walk into a church and see a pastor stand on the pulpit and say "homosexuality is a choice, and we respect and welcome people who have made this decision because we respect the personal autonomy of individuals". but, in most cases i don't think it's that clear cut. the choice is in not rejecting the stimulus that's developed. i don't think god has much to do with it, but if you locked this kid in a room and made him watch and masturbate to heterosexual porn for a month, he's likely to come out fully bisexual. but, that approach wouldn't respect his rights as an individual - that is, it wouldn't respect his choice not to conform and we should be supporting choices not to conform when they are real...
ultimately, what this kid has to come to terms with is that he has to find his own path from his parents. it's something a lot of people go through due to disagreements over lifestyle, career choices and a thousand other things. sucks, but he's gotta move on and leave them behind.
