I actually think the Andy lines were more about him trying to be sensitive to what had become apparent to everyone; Jack and Ianto were in love and in a very open, visible relationship. If you're going to inform the family of Ianto's death, you probably would want to know if they knew their brother was gay so you don't put your foot into it, or, so you can offer your proper condolences. Plus, Jack wasn't with them, so Andy probably wondered if that might come up as well.

At least that's how I'm choosing to see that, because I fucking love PC Andy and I refuse to believe he would give a rats ass about Ianto's sexual status (unless he was getting some from Ianto but that's a whole 'nother story)