you can use an action to read the scroll and cast its spell without providing any material components.

For the purposes of spellcasting it is still you who cast that spell, unless the text of the magic item says "as if you had cast spell". See the description of Censer of Controlling Air Elementals.

While incense is burning in this censer, you can use an action to speak the censer’s command word and summon an air elemental, as if you had cast the conjure elemental spell. The censer can’t be used this way again until the next dawn.

Are scrolls and magic items that cast spells all still casting spells?

Yes, based on the general rules of casting spell scrolls. So it follows the rules on casting bonus actions on your turn where you can only cast cantrips with a casting time of 1 action if you cast a bonus action spell (whether using your spell slots, racial features, spell scrolls, or other game features that specify "you cast" a spell).