Keywords Finder

I've tried to solve https://py.checkio.org/en/mission/words-finder/ and dont't understand why checkio("Hello World! Or LOL", "hell world or lo") == "<span>Hello</span> <span>World</span>! <span>Or</span> <span>LO</span>L" !? I think "Hello" + keyword "hell" == <span>Hell</span>