You're right; it's been a long while since I did that fight, so the fine details escape me. Thank you for jogging my memory. (I'm not perfect, c'mon...)
Ehh... well, Zenos' ability to use magicks at Yuzuka Manor may be attributed to the original intent of Aulus' research: imbuing Garleans with the ability to wield magicks. Fordola specifically notes that such a treatment would be useless on her since she's not a Garlean, but Zenos explains that's not what was done to her and that the ability to wield magicks pales in comparison. We don't see anything else.
Ultimately there's not really enough information to draw a conclusion. Did Zenos have Aulus modify him so he could wield magicks prior to our bout in Ala Mhigo? (Probably, because I faintly recall some lighting swords raining down on us back in Rhalgr's Reach.) Was the Resonant Echo responsible for his ability to wield magicks? (Unlikely.) Why did they need an Echo user to make Resonants? What's the connection between Hyptertuning and the Resonant Echo, if any? What is Hypertuning?
I hope all these questions are answered at some point.