Earlier quoted context omitted.
Let's oversimplify for the sake of showing the calculation... There are 4 stocks in the world, A, B, and C, and D, all trading at $25. I invest $100, buying $25 in each. Now lets say that I know for sure that stock D will go down because I'm going to whack the CEO. So I sell my $25 of D, and put it in A, B and C (A stake of $33.33 in each - let's assume fractional shares are ok.) If Stock D goes to 0, while the other…
All of your profit in this scenario comes from the market going up, not D going down. That's not a short (or synthetic short) position.
Think of it this way - in both cases you're selling today, and buying later. The only difference is the "hold the whole market first" strategy requires more capital. (There are market technical differences too, but for short time periods these aren't as significant)