I somehow just got this

[GlaceonHybrid]

I feel like I just solved the Di Vinci code oh my Arceus. Lugia is based of the Native American Thunderbird, that's why it's psychic/flying and not water/flying.

Thunderbirds are birds of storms, but are huge and also incredibly smart, being able to speak to humans and are renown for their knowledge. They are known only to be seen with storms.

Sound familiar? Now let's look at Lugia's entries

(note, these are all direct quotes from the pokedex, I own none of what's about to be seen)

Gold   It is said that it quietly spends its time deep at the bottom of the sea because its powers are too strong.
Silver   It is said to be the guardian of the seas. It is rumored to have been seen on the night of a storm.
Crystal   It has an incredible ability to calm raging storms. It is said that LUGIA appears when storms start.
Ruby
Sapphire   LUGIA's wings pack devastating power - a light fluttering of its wings can blow apart regular houses. As a result, this POKéMON chooses to live out of sight deep under the sea.
FireRed   It is said to be the guardian of the seas. It is rumored to have been seen on the night of a storm.
LeafGreen   It is said that it quietly spends its time deep at the bottom of the sea because its powers are too strong.
Emerald   LUGIA is so powerful even a light fluttering of its wings can blow apart houses. As a result, it chooses to live out of sight deep under the sea.
Platinum   It sleeps in a deep-sea trench. If it flaps its wings, it is said to cause a 40-day storm.
HeartGold   It is said that it quietly spends its time deep at the bottom of the sea because its powers are too strong.
SoulSilver   It is said to be the guardian of the seas. It is rumored to have been seen on the night of a storm.

Black/White/Black 2/White-It sleeps in a deep-sea trench. If it flaps its wings, it is said to cause a 40-day storm.

X   It sleeps in a deep-sea trench. If it flaps its wings, it is said to cause a 40-day storm.
Y   It is said to be the guardian of the seas. It is rumored to have been seen on the night of a storm.

Omega Ruby/Alpha Sapphire-Lugia's wings pack devastating power—a light fluttering of its wings can blow apart regular houses. As a result, this Pokémon chooses to live out of sight deep under the sea.

(end of direct quotes)

So my conclusion is that Lugia is a Psychic/Water type because Thunderbirds are incredibly smart and able to directly communicate with humans, much like the Psychic type Pokemon with moves like telepathy and mind reader.

[SirBlaziken]

I honestly thought that Zapdos was based on the thunderbird, but it still could be, maybe off a different sort of mythos. Nonetheless, that's a really cool connection I would not have made myself. Nice job!

[GlaceonHybrid]

I honestly thought that Zapdos was based on the thunderbird, but it still could be, maybe off a different sort of mythos. Nonetheless, that's a really cool connection I would not have made myself. Nice job!

I believe Zapdos is more based of the lighting part of the mythos, summoning lightning and shooting it from its beak. Lugia seems to be more based of the storm part of it.