Yes to both.
For number one, I think it's intended to refer to a) the ability to cast spells in the first place and b)to spellcasting class, as I don't believe there are any magic items which require you to be able to cast a specific spell, only that require you to be able to cast spells, and, more specifically, belong to the class that the item requires.
Regarding number two, the easiest example is a Holy Avenger(which requires you to be a paladin to attune to it in the first place):
While you hold the drawn sword, it creates an aura in a 10-foot radius around you. You and all creatures friendly to you in the aura have advantage on saving throws against spells and other magical effects. If you have 17 or more levels in the paladin class, the radius of the aura increases to 30 feet.
The artificer feature should allow you to ignore both of those requirements.
As a side note, this feature allows you to use a few magic items that are normally fairly locked down, namely a Mind Lash, which requires attunement by an illithid.