Maybe. How big are they?

From Penn State,.,

“The artillery fungus is quite small – the fruiting bodies are about 1/10 of an inch across and are very difficult to see in the mulch. Artillery fungi are much smaller than the bird's nest fungus with which it may be mistaken. By the way, the bird's nest fungus does not actively shoot its spores – those little "eggs" of the bird's nest fungus are splashed out by raindrops, and thus are called "splash cups."”

The whole article…

http://personal.psu.edu/users/d/d/ddd2/

tj

Unless the mulch was touching something made of wooden which you wanted to preserve there was really no reason to remove it. These fungi are natural decayers of dead wood. I'm afraid you gave yourself unnecessary work and expense trying to eradicate it. It doesn't do any harm at all to you or your garden.

It doesn’t do any harm to the gardens but they spew black spots that get on the side of the house, walkways, cars etc and are nearly impossible to remove

If these are as big as I think they are, they are bird’s nest fungi which do not shoot spores.

tj