Magus - Evil Eye multiclass question

Just to clarify something, I have seen a lot of people talking about Esoteric Eye being an overpowered 1st level dip feature. While I do think this class is great for a wizard to dip in at 1st level for AC, Con save proficiency, and Int based spellcasting, the Esoteric Eye specifically says, "Advantage on your Magus spell attacks against it and it has Disadvantage on saving throws against your Magus spells", this to me pretty clearly says that it does not work with spells gained from another classes spellcasting feature. Is this the intended reading of the feature? Or is it actually intended to work on spells gained from other classes?

Example: A level 4(1 Magus/3 Wizard) who uses Esoteric Eye then casts Hold Person(a level 2 spell gained from their wizard class levels) against the target of Esoteric Eye. Would the target have disadvantage on the saving throw against this spell? 

I don't believe it works with spells gained from other classes. I read it as the spell must come through the Magus class in order for the Esoteric Eye to work. So the in the example you used, Hold Person would not gain the Disadvantage for the Saving Throw.

I like multiclassing into Wizard when I play the Fighter Eldritch Knight. I've always treated the spells gained through the Eldritch Knight subclass can't be swapped out like the Wizard's spells each day.

Quote from PavelRykov >>

I like multiclassing into Wizard when I play the Fighter Eldritch Knight. I've always treated the spells gained through the Eldritch Knight subclass can't be swapped out like the Wizard's spells each day.

While this is true, it's a totally separate issue from the question of whether a spell counts as "a Wizard spell" or "a Cleric spell" or "a Magus spell".

The official answer to that question is in this Sage Advice answer, which essentially says that it counts as "a X spell" if it's on the class list for class X, regardless of how you gained access to the spell. Thus, when it says something like "saving throws against your Magus spells", it should be interpreted as "saving throws against spells you cast that are on the Magus class list".

However, this answer was a surprise to a lot of people when it was published, since prior to that most people were treating "a Wizard spell" as meaning "a spell you gained access to through Wizard class features" and many people still play this way. The Magus class is third-party content and may very well have been written by people who interpret it that way rather than the way it's written in the Sage Advice answer.