Sakai studied finance / business, as was shown during the chapters that involved his time at college. KV was also written way and is set in a time way before most people are as security literate as they are now (even today, security training for employees is a big thing for large companies, since social hacking is the leading reason for breaches). The phishing attack was sophisticated enough to easily trick people who aren't well versed in security.
With all that said, Sakai is still way too loose with his money, which is at the same time typical and atypical of angel investors. (The ways his looseness is expressed is a bit unusual...)
full disclosure, i tl the series.