Given AAPL is at an all-time high they would've made money if they held onto it and not sold at a loss.

As most stock market indexes have a general upward trend, more people make money then lose. Though I still wouldn't recommend investing what you can't afford to lose or can put aside for the long term as you'll stand a better chance to make money if you can hold onto it through the downswings. Obviously you can still lose by investing in the wrong company, but you can mitigate your risk by spreading out investments over multiple companies/markets. There's a much lower chance of losing money on shares in the long term if you're sufficiently diversified.