Santino is an advanced tool-maker, learning to create concrete missiles through its own initiative. And what's more, he showed the ability to plan for the future based on a predicted state of mind, rather than the one he was currently experiencing.
I haven't seen other reports about Santino discuss this issue - he didn't just plan for the future but did so with a self-awareness of what his future state of mind would be. If he thought in words it would have meant him thinking, "Humans will show up today, I will be antagonized, I will want to throw something at them, nothing to throw at them is presently available, so I will make things and store them for when I am angry." The fact that Santino doesn't have mental language capability makes it even more impressive that he could understand these concepts without words to guide him.
More evidence that intelligent animals like the great apes shouldn't just be used as our playthings or medical subjects except under circumstances we'd apply to human child subjects.