I'm pretty sure that if there is such a tweet that says this feat gives someone a spell slot that it is either A) using the same shorthand that can be misunderstood if the context isn't know, or B) actually mentions that said spell slot is limited how you can use it (to cast this one spell only), not just +1 to the number of 1st level spell slots you have.
It was actually in Sage Advice, not a tweet: https://dnd.wizards.com/articles/features/sageadvice_feats
And I stand partially-corrected. If you choose your own class and you're a sorcerer or bard, it pretty much works as I described. It gets added to your spells known and you can cast it with whatever slots you choose. If you're a prepared caster, it gets added to your known spells (which is only helpful for a wizard) but has no effect on your prepared spells. But you can still cast it with any slots if you have it prepared.
If you pick a different class, then you're limited to the once per day, special slot only.