You're conflating concepts. The funny thing is, your argument about price behavior is completely irrelavant to the article's points.
Is the article claiming that there is less of a probability for the stock price to return to its previous level of $10 because that would require a 100% gain versus only the 50% drop it took to $5? Then yes it is an example of the traders fallacy.
How about you explain to me why you think it would be harder (less probable) for the stock to return to $10?