I think your are reading the requirement backwards (Masked-man fallacy).
We know the magic action now has 3 distinct sub-type types. (much like the attack action)
1) you cast a spell OR
2) you use a feature that requires a magic action to be activated OR
3) you use a magic item that requires a magic action to be activated
Thief Fast Hands lets you do (3) as a bonus action:
"take the Magic action to use a magic item that requires that action" ["that action"="the Magic action"]
This clearly applies to (3), but not (1) or (2).
Nowhere in scroll does it say it requires the magic action. It does says that you both "read the scroll" AND "cast the spell" using the spell's normal casting time. So you cannot separate these events.
Furthermore, multiple people cannot read the scroll (unless this is specified as part of the scroll):
"
Spell Scrolls and some other magic items contain spells that can be
cast without a spell slot. The description of such an item
specifies how many times a spell can be cast from it." Since the text for scroll creation describe the process as a spell casting transfer, there is no reason to assume more than once.
So is reading a scroll considered casting a spell? (or using a magic device?) The description of casting a spell in chapter 7 tells us:
"Before you can cast a spell, you must have the spell prepared in your mind or have access to the spell from a magic item, such as a
Spell Scroll."
At least for 2024, a DM reading the rule can easily rule that reading a scroll enables one to cast a spell that is not prepared in your mind.
When you compare the scroll description to the D&D beyond 2024 magic items from Uni-horn, every single magic power item begins with this text "As a
Magic action, you can ......"
There is one item that is distinctly different: "This Mace has 6 charges and regains 1d6 expended charges daily at dawn. While holding the Mace, you can expend 1 of its charges to cast
Summon Celestial ". It doe NOT say 'as a magic action ...."; it says you can use a charge to cast. The hat is similar but weird
The scroll description is written the same way -- it uses the word "cast" not "as a magic action".