"Good" basically reduces to "do what your users want".To be fair, PG makes the same connection in the essay, albeit in the opposite direction: "Make something people want. Don't worry too much about making money. What you've got is a description of a charity." And charity = good.
Arguably, tobacco companies make something people really, really want, but they do not fit the definition of charity or good, probably because while people really want tobacco, it's not in their long-term interests. In other words, there's a gap between what people want and what they should want, and the tobacco companies exploit this gap. So PG's description fits more things than just charities -- and he really doesn't argue otherwise; he simply chooses not to consider it in the essay.
There have been plenty of successful startups that similarly satisfy "Make something people want" but are of questionable benefit to their users' long-term interests: gambling, adult sites, online games, etc. Whether or not these endeavors constitute "evil" is, of course, a value judgment and depends on what you consider a long-term benefit. (The very idea that "good" and "evil" could be phrased in terms of short- and long-term benefits is interesting...)