Yes and no as there is difference but not in way that matters in that conversation ,if you are ready to kill somone for religion (well not only religion but in that case) pretty much good prove that you are zealot.
I'd argue not quite, as zealotry covers much wider range of activities and I feel in order to be considered one you'd need to be much more militant about far lesser things. To reuse the earlier example, if someone gets angered by the act of desecrating remains of a person they loved to the point they kill the person responsible, I don't think this proves they're cold blooded murderer in general.
Mind you, I'd agree Leliana displays zeal throughout the game and so it's probably fair to consider her one. But not because of that one particular act.