i reckon, nuclear way happened, killing all the humans. Ponies mutated from the radiation to grow wings, gain magic, and become sentient. this would leave some human relics, like the tools you see as well as dictionaries which could have led to the basis of their language. the continent would have changed slightly due to continental drift and stuff, everything glows because radiation, and Equestria High is a completely universe where humans didn`t wipe them selves out but somehow became similar to equestrian ponies.
(not sure if this is a forum place for this thing, but i don`t know where stuff is supposed to be)
(could some staff move it to Sugarcube corner?)