R.E.N. Spells Ren
Veteran
The quote did continue with this: "The Targaryans can tolerate a bit more heat than most ordinary people, they like really hot baths and things like that, but that doesn't mean they're totally immune to fire, no."
Targaryens simply have a high tolerance for heat, just as the Starks do for cold.
I can only remember two occasions right now; the dragons and burning the Dothraki khalasars. The second could also be explained as blood magic.
The third display of her fire invincibility was the house of the undying. The two displays of high heat tolerance that I'm thinking of are when she picked up those hot dragon eggs, her hands didn't burn but her assistant's did and when she got in that hot ass bath in the first episode with her assistants telling her to wait cuz it's too hot.
All Targaryens aren't immune to fire and don't have high heat tolerances...Viserys showed us this. Not only with his golden crown but also when he's sitting in the tub with the Doreah, she lets the hot wax from the candle she's holding drip on his chest and he's clearly in pain.