I would say love and deeper love!
What you did was not just love in words but in action, and also an act of investment.

When correction comes without patience and tolerance, it can be like weapons formed against one, which certainly will not prosper. It is destructive criticism.

Constructive criticism is love with evidence. You showed him what it means to be better. It is emotional intelligence in practice.

I had a friend who sometimes throws corrections on people, especially those she expects to be better, still on the quest to help them improve. At times she leaves them to figure it out themselves. Her intention was good, but her approach often led to tension. It took humility and maturity for me to first be reachable before being teachable.

Being a victim of this experience, I came to understand that while everyone can be teachable not everyone is reachable. Then, I deliberately began treating everyone that I think needs corrections like babies.

In learning how to talk and walk anew, I hold their hands gently and mold their words carefully, teaching them how to walk and talk without dragging them or leaving them to figure it out by themselves. At times, I get stuck in the valley and shadows of repetition, yet I choose patience and love over anger.

With this approach applied, I believe people would become more teachable and reachable in this world, because who on earth would not like to be loved?

Finally, you did not just do this, nor just help him design better slides, but you also designed a healthy way to grow together. I'm certain he will do the same for others.
And together, we grow.