English is a very ambiguous language.
Your powers will get Storm Cell bonuses as long as they target enemies that are inside of a Storm Cell. However, only your Storm Cell will proc High Wind and Lightning from your Powers.
In the contact of this sentence it could be referring to that fact that there are multiple bonuses from Storm Cell that will apply to any storm blast power in its effects. The plural on bonuses could also mean multiple Storm Cells, or both.
While it is good information, and I was happy to learn this info, due to the nature of our language it is not a precise answer and I like to understand how things work and not guess.