You really have to ask? I know I'd be annoyed if I found things had been put in my bag without my knowledge.

Lets take the example to an extreme, what if the bag which had spilled its contents had contained an innocent looking item which actually contained illegal drugs, it mistakenly gets placed in your bag, and then at your destination you get stopped by customs and searched........ I would like to see you talk your way out of that one. ".....But officer, I have never seen that before in my life"