Thanks for the question @Habib_Ullah!
That behaviour is as expected. App Search leans towards recall over precision, so it casts a wider net. There isn't a way to disable that behaviour, though you can use some Lucene Query Syntax functions to refine your search,.
In your example, it will also look for terms that are similar to "coke" - so in this case, the "oke" in smoked is the closest match in your document set. Of course, if you did have any documents with the term "coke", those would surface first (if not, try adjusting your relevance tuning settings).
Hope that helps,