Even my experienced D&D GM never had a clear answer to "are psionic powers considered magic?". It led to some very ridiculous situations, like our ninja being unable to use his ki powers inside a dimensional-locked antimagic sphere but our psion casually teleporting there with the whole team in a bag of holding, or enemy psionics manifesting their psionic powers and leaving no magically detectable trace of them (even their summons had no magical aura!).
As far as I dug into the Pathfinder rules, I found nothing clear either.
Just for the sake of breaking the traditional fighter-mage-thief comp and truly have fun in a new game, one of my friends wants this question answered to play a psionic class without breaking the rules.
What category (spells, spell-like abilities, supernatural abilities or extraordinary abilities) do psionic powers fit ?
Best Answer
Psionic powers have their own category
The rules for psionic powers state that psionic powers are like spells, with a few differences, explained in those rules. Also psionic powers are considered psi-like abilities:
Psi-like, Supernatural and Extraordinary Abilities
Psionic powers can be emulated by creatures, which works just as if the creature had a psionic class that grants psionic powers. Psi-like Abilities work very similarly to spell-like abilities.
Supernatural abilities don't have that restriction. Those abilities work emulating a specific power and follow the same restrictions from the bestiary..
Extraordinary abilities are rarely magical or psionic in their nature. So there is no difference here.
This is explained in detail on the chapter about Special Abilities.
Which means that creatures and characters can have Psi-like abilitie in addition to Extraordinary, Supernatural, and Spell-like abilities. Those special abilities that emulate a psionic power are either Psi-like abilities or Supernatural abilities.
The GM can rule differently
However, in your example, it seems like your GM was using the optional rule for Psionics and Magic are different. The psionic rules from Dreamscarred Press presents the GM with two options regarding how psionic powers should work on the game mechanics:
If you decide that Psionic powers are Magic, you are presented with rules to combine psionics and magic, that aims for a better game balance and for an easy mix of magic and psionics on the same campaign. Basically, psionics and magic are only different on their source, the result (magic) is the same. Spell resistance will apply against psionic powers, psionic powers are negated inside an anti-magic zone, and Spellcraft can be used to identify psionic powers, etc.
The rule of thumb is that they work exactly the same (called psionics–magic transparency), and anything that grants spell resistance or increased saves versus spells will work against psionic powers.
If you decide that Psionics and Magic are different (again, a optional rule), it will explain the rules for psionics powers being different from magic (under Variant: psionics As Different), This can be used the default rule on campaign settings such as Dark Sun that, back in 2nd edition, had psionic powers being different from magic for setting-specific reasons. And it is suggested to be used on campaigns where most people and creatures uses psionics powers instead of magic.
If you treat them as different things, then creatures with spell resistance are less of a challenge to your players if none of them uses magic, in constrast, a creature with psionic resistance becomes a greater threat to your players.
So, it's best that you consult with him what rule he is actually using on his table. Or that if he even read those rules and wasn't simply ruling things without a backup on the ruleset.