Truth is proof, and the article contains no details to establish this absolutely. So, we are left with supposition.
This wasn't an isolated man with nothing to live for - while his career in AI was over, he'd left it to pursue a moral agenda. Suicide is not likely until AFTER he testifies and discharged this.
The fact he supposedly had documents and a testimony that could heavily harm a company is enough to make it very likely his death was the cost of doing business - why pay a billion in a court case when you can pay a million for a professional hit?
On the balance of probabilities, it looks more likely to be like foul play. As they say, Epstein didn't kill himself.