At that time, it was only run by two people, Poramin, Lead-developer, and his other co-founder, Gary.
Reuben and Gary were very lean, and he got "wowed" now thinking that this ZCoin technology, was pretty good.
It was actually based on the Zero coin paper, which was one very well peer review, had one interesting concept, but still had nobody else to support them.
So then he decided to help them because it sounds fun, and why not just help them and see where the project would go, started helping them and kind of became something like a community manager.
While he was the community manager for ZCoin, he got to know Poramin and Gary, it was kind of like a bittersweet story, but anyways, that was how he got involved in all this ZCoin thing and was probably the first employee, but didn't actually got hired, got interested and helped them.
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From @stammy