If it was the old fashioned real creosote then yes, it will certainly kill off any leaves touched by it, despite the hose. If it was one of the modern creasote substitues then you may be lucky. The old creosote stuff by the way is no longer legal.

Even the modern creocote (I think that is what they cal it now) is pretty vicious. Not only that the stuff will have got into the soil where it will continue to cause problems.