The term "Mythicals" does indeed refer to event-only Pokemon. It's actually a direct translation from the Japanese term "Maboroshi Pokemon". Legendaries on the other hand is called "Densetsu Pokemon".
Maboroshi and Legendaries are two different categories to the Japanese officials -- recall we could use one legendary in the 2010 World Championships, but no maboroshi could be entered.
I suspect the term "Event Pokemon" is confusing by itself since Shiny Pichu is an event too. That's why PUSA decided to follow the Japanese official and reclassify maboroshi as "Mythicals" in order to distinguish them from legendaries obtainable in-game.
(By the same reasoning, Zorua and Zoroark should not be Mythicals because they can breed and evolve. (The jury is still out for Phione) They are not legendaries either, so they'll be classified as normal Pokemon.)
Maboroshi and Legendaries are two different categories to the Japanese officials -- recall we could use one legendary in the 2010 World Championships, but no maboroshi could be entered.
I suspect the term "Event Pokemon" is confusing by itself since Shiny Pichu is an event too. That's why PUSA decided to follow the Japanese official and reclassify maboroshi as "Mythicals" in order to distinguish them from legendaries obtainable in-game.
(By the same reasoning, Zorua and Zoroark should not be Mythicals because they can breed and evolve. (The jury is still out for Phione) They are not legendaries either, so they'll be classified as normal Pokemon.)