What it means is that unlike lesser simulacrum (the spell the ability immulates) the duplicate is entirely real once created. Normally a simulacrum is just an illusion over an animated ice sculpture... which quite honestly should have more drawbacks than it does... but that’s a different topic...
Alchemical simulacrum creates a real flesh and blood clone that lasts for 1hour/level before reverting to a shapeless blob of flesh. The process to create it is a supernatural effect, but once created it functions entirely as a normal creature. This means it very well can waltz into an antimagic field without being destroyed, unlike its lesser simulacrum counterpart.
As for the creature type, same as the original creature.