I think my confusion or questioning here is the presentation of the information. Once you explained it, I have no problem following. Let me elaborate to what I refer using Referees Guide:
Under Combat you may take one of a list of Combat Actions. A subset of this list includes an Attack, a Combat Manoeuvre (these British spellings are killing me ... now I know how you must feel reading American English lol) or Use a Spell ability. In the same column you define Critical Success or Failure as:
Critical Success or Failure: On a critical success, a combat manoeuvre (i.e. stun, disarm, grapple) is automatically performed. On a critical failure, the weapon is damaged.
The problem I have with this layout is that there are several things in this column that could result in a critical roll.
In the right column you define/redefine Magic's definition of Critical Success or Failure. Now no one is going to confuse hitting with a sword and spell casting but if you are quickly looking up the impact of a crtical roll in combat you could miss this. For me, the layout is a bit of logical disonance.
Let me further explain because the above is nitpicky.
Combat manoeuvre includes Grapple which unlike the others provides an example opposed roll. There is a chance of critical roll during a combat manoeuvre and that is where I went down some wrong path thinking the verbiage about critical success or failure was related to the Combat Manoeuvre roll.
This is an unnecessarily long description of my mistake to propose a clarification and based on Nameless Designers response above a further clarification ... something like:
Critical Attack Success or Failure: On a critical success, a combat manoeuvre (i.e. stun, disarm, grapple) is automatically performed as appropriate for the situation. On a critical failure, the weapon is damaged.
Using a ranged weapon, you could argue something like Disarm as the arrow hits the opponent's hand and they drop the weapon. You will have to be clever to argue Grapple 40 feet away (I would never say 'never' to the internet as we know someone would prove me wrong).
If you really wanted to be consistent you could change magic critical success language to: Critical Magic Success or Failure