This question is on the Spell Thief, a homebrew class presented by Middle Finger of Vecna, and its ability to steal spells.
When the ability says "innate spellcasting feature" this means things like Dragons breath attacks and Beholders ray attacks right or a spell via Magic Initiate feat right? If so and then take for example the Spell Thief stole a Dragon's Breath attack, does it mean the dragon has a to roll to recharge its breath attack right before it can use it again thus literally robbing it of its use temporarily?