You have it partly right, but you get it wrong and twist it to bigotry IMO.
First, the exact biological issues in homosexuality are not understood - but some issues are.
For an example of the complications, take the very simple test of identical twins.
If homosexuality is genetic, all identical twins will be both or neither gay. If it's not, all twins will be as randomly gay or not gay from each other as from anyone.
So, which is it? The answer is, a twin is FAR MORE LIKELY to match his twin at being gay or not gay than random chance (IIRC 60%?) - and far from 100%.
So, huh?
What you get right is saying biologists suspect something more complex like a genetic trait that *has a chance* to cause homosexuality.
That might mean:
No genetic trait + no mystery trigger = heterosexual
No genetic trait + mystery trigger = heterosexual
Genetic trait + no mystery trigger = heterosexual
Genetic trait + mystery trigger = homosexual
One thing that seems clear is that generally, homosexuality IS there very early - seemingly as early as tests can tell (around age 5 if not earlier) with indications it's earlier.
You get it wrong, though, implying something like 'a straight person for some reason decided to have a homosexual act, and it turns him gay.'
There are other things that aren't explained yet, like a correlation of which finger is longer to homosexuality, that have theories around hormones being involved in a trigger.
Your main point is wrong, that the 'biological' is 'PC and wrong'. It's right.
The old bigotry about homosexuality was that 'gays are just like other people except that just like those who rape steal and murder, they choose to do evil things.'
People didn't understand why people did those things - they were just evil, 'perverted'.
They did not understand that for gays, their sexual feelings are just as built in and natural as heterosexuals' feelings are from a very young age - the issue is 'biological'.
The actual history you did not mention is that a 'PC' line was calling it 'lifestyle choice' - society had a lot of existing views that had tolerance for that issue, in terms of 'some people prefer to be more promiscuous, some less, some to date old or another race or have multiple partners' - all variations that had become 'accepted' and so it easily fit to say 'hey, let gays make their choice too'. But that's what was misleading and shown wrong by showing how it is more biology than 'choice' as an orientation.
Of course, sex acts are choices - the issue there, though, is inconsistent rules for gays than for heterosexuals, based on the bigotry that gays are 'wrong', 'evil', 'perverted'.