Typing in the search field on iOS 8 will fetch web results as well, which means some web server is being hit with what you're typing. Spotlight on Yosemite is getting a similar feature as well.
I'd suspect that at least on Yosemite you'll be able to disable the web search. You can already choose to chop out huge sections of Spotlight's optional functionality on Mavericks, so I don't see why that'd change come Yosemite.
