The cache mentioned in the opening post was hidden in February, so the cache hider could have been unaware of it's existence when it was hidden. It is also an area where the plant is common enough that the hider felt local cachers would notice it without warning. It could be that the hider didn't want to give the cache location away by mentioning it was hidden near the plants.
I disagree. The fact that the cache was named "Sting" means that the cacher knew EXACTLY what plants were in the area, and probably thought it would be a great laugh to see the logs about people getting "stung".