Peppermint flavoring does not have to be from peppermint oil. There are other ways to make the flavor, so your peppermint may not be oil. I have no idea why soybean oil would be used for anything in juice.
Also, I have used oils in making juice and it requires very little. So I would use a tiny amount of natural peppermint oil to get the same flavor as compared to artificial peppermint flavoring.
But, I am a former smoker and vaping is a reduced harm process over the burning tobacco. So just about anything I put in my juice is much less harmful than the smoke I used to inhale. If I was not a former smoker, I would seriously question why I would be wanting to inhale something that may be harmful even if it is less harmful than smoke that I had never inhaled.
I am not under any illusion that vaping is perfectly safe, so the thought of a nonsmoker picking up the vaping habit is an odd one to me. If there is a need to self-medicate with nicotine, there are safer ways to do so than vaping. It does not look cool and there are plenty of much more fantastic ways to taste flavors than sucking on mini fog machines like eating them.