Was trying to figure out what mimosa hostilis means and did a quick search and I found this:

Mimosa derives from the Latin word mimus, meaning to imitate.
Hostilis derives from Latin and means enemy.

So it would seem it means "To imitate enemy"

[from New Latin, probably from Latin mīmus mime, because the plant's sensitivity to touch imitates the similar reaction of animals]

hostilis - hostile or enemy, armed

I think it's referring to the idea that unlike other Mimosa plants which have the ability to retract their leaves when a predator touches them, this one is armed with a defence (in this case the DMT) and so it is much more harmful and "hostile" if predators try to eat it than the other mimosas. I guess Mimosa Hostilis is just the tough guy of the lot.

Doesn't mimosa hostilis have giant spines all over it? That seems pretty hostile. Most scientific names are mainly historical anyways.

Don't know if it does. If so, then that's probably the reason why.