It hints at the fact that he'd already found, and lost, his true love. Besides, it's probably just covering up for the fact that she'd not had an actual 'out' character in all the books, which helped it to appeal to the middle of the road mainstream type parents. Then she follows up by appeasing the (ever too easily at times) offended gay community by announcing that one of the characters had secretly been gay all the time, pulling the rabbit out of a hat type of thing.
There's a t-shirt idea, Dumbledore pulling a pink rabbit out of a hat, with the caption "Surprise!"

And come on, ship the damn t-shirts to the rest of the world, I want the orange one!