The Summoner quest that gives you Dreadwyrm Trance has a slightly different explanation as well. If you're from 1.0 it says you were exposed to Bahamut aether by being at Cartenau. If you weren't, it explains that basically everyone was exposed to Bahamut's aether because of the Calamity no matter where they were at the time. The Lore Book even supports this and is almost cheeky when it explains that technically everyone who was exposed to Bahamut's aether can cast Teraflare if they had the right training...