That's more a Facebook thing than an iOS thing. FB is a memory hog and is always refreshing feeds.
It is not just FB though....that was just a specific example I was giving. It happens on a lot of websites.
For me, it has been an issue since day 1. I remember when I got my first iPad and bought something off of eBay. After I confirmed my purchase, my browser crashed and when I opened it back up, it refreshed the page and resulted in a second purchase. I was lucky and the seller cancelled the second one for me.
And at the same time, it is an iOS thing. I have never experienced the same thing happening on a laptop or desktop.