Maybe the real reason guy didn't join, although compensation is "good" is not that good? Maybe he saw the writing on the wall and didn't want to go for a "good" salary only to be forced to look for another job in next few months when funding money expire? Maybe he didn't like the prospect of working 60+ hours weeks? Maybe he just doesn't like 2x startup culture?
There are a million valid reason why someone wouldn't want to join startup, even for a "competitive" salary, and it has nothing to do with having spine or not. And he's not obliged to tell a real reason to anyone, so "too risky" is as good as an excuse as anything.