If it's a fair coin you can make money off it, and convince yourself you can predict the "market" "because the coin is biased" ... but it's just 'luck' (ie statistical anomaly).

It evens out in the long run so this doesn't apply to this person's trading.

I think that's a statistical misunderstanding. It's likely to even out; across a population it will even out. An individual however can get "more heads than tails" by chance.