The article barely mentions this, and I haven't seen comments here mentioning it, but a huge factor in determining identities is one's writing style. In fact, analyzing the way people speak and write is its own science (linguistic forensics) and is also used by law enforcement (though can realistically be done by anyone with OSINT and basic understanding of individual linguistic patterns.) Dead giveaways are especially if you consistently misspell a certain word or use a certain emoticon or uncommon phrase or word, it's like a linguistic footprint. If Andy123 on Reddit and XxwhateverxX both spell appearance as appearence and both say booyah and both spell :) as (:, then it is much easier to tell that they may be the same person. This is something that you must be aware of, as well as giving out personal information like country of origin, amount of pets, place of work, etc.