App have 7-8 different methods of running in the background. Background App Refresh is only one of them. Push notification from APN can start an app in the background so it updates it data, like if you are watching a stock.
I'd be curious to see the rest of the battery life screen page. There is a lot of stuff running on the iPhone, that doesn't make its usage a noticeable portion of the battery. For example if your battery drops from 100% to 98% over a few hours in standby there might be something that stands out using 80% battery or something like that, but 80% of 2% total isn't a lot. Dunno if that makes sense.
However first if you don't use the Stocks app, then delete it. If you do, make sure its closed in out of the background apps and notifications are off. If thats unreasonable because you track a bunch of stock then expect it to run in the background a lot.
For some people the stocks app is incredibly important and it not being as up to date as possible could result in the loss of a substantial amount of money.
It might be a bug but if you Google search this you'll find results starting back in 2012, then 2013, 2014...etc...