The phrasing in 2014 was open to interpretation. I always interpreted it the generous way because it made the feat more attractive.
Using actual RAW in 2014 it depends on what class you are talking about.
You "learn" a spell according to the 2014 feat descripton, meaning you "know" it. This means 2014 Eldritch Knights, Arcane Tricksters, Rangers, Bards, Sorcerers and Warlocks can cast the spell using their slots or Pact Magic. Artificers, Clerics, Druids, Paladins and Wizards can't because they can only use spell slots to cast spells they have "prepared" (unless they have a multiclass into one of the other classes).