It's also possible that the person was referring to recently manured as fresh (versus rotted) manure being applied to the soil which is more likely to kill all plants and seeds. The ammonia content is very high in fresh, hot off the press, manure and plants can't tolerate it.
I apply fresh manure every fall to my veg beds and won't plant anything until spring when it's had a chance to mellow. My fall garlic beds get an application of old manure that I save just for that purpose.