False. They get 2 in almost all situations.
It is rare for lust to be used solely on the last 40 seconds of a boss, which is the only case where a mage would get 1 lust. Even if you lust 90 seconds in for a burn phase, the mage can get lust again the next burn phase while the rest of the raid can't.
This meme needs to die, it's being perpetuated by people who are terrible at this game and have no idea how to play any spec, let alone fire.