Nice catch! You might just be right. MIGHT.
I don't know that Power Memory is necessarily *the* Zygarde Cell card, just because it's pictured on the card, if you know what I mean. There is going to be a Zygarde 10% card confirmed in this set (we only have an image from the booster box); so I wouldn't totally rule out a Zygarde Cell card, but that being said because we don't know the game mechanics I can't rule it in either.
I think it would be a shame if Zygarde 10%, 50%, and Perfect Forme didn't somehow interact. The idea of Zygarde being made of Cells could be implemented in so many ways Game Mechanics wise, and I'd like to see them do something cool with the cards.
Also note though that cards can't necessarily be used to determine game mechanics. Imagine we saw the "mega evolution rule" before we knew about in game mega mechanics. One mega per battle (the in game "restriction") doesn't really correlate to not being able to attack the turn you mega evolve (technically the TCG "restriction").
Also in my (probably amateur) opinion some people are overhyping Zygarde-EX Perfect a bit. I don't see it being that great, even with Carbink and Power Memory... a new deck archetype, yes. But a Worlds winning one? Idk about that. The good news for Zygarde EX is hitting M-Manectric for weakness (and thus, hopefully not having to discard for Power Memory if a damage modifier is on the feild).
Overall though I must say I'm really looking forward to this set!
Can anyone else confirm that a trainer card with an attack exists before this?