I've seen this as well, and yes, it freaked me out Uninstalled Chrome/Youtube app, 5-6 months later reinstall it, it automatically logs me in-- and I was like

I've seen this as well, and yes, it freaked me out Uninstalled Chrome/Youtube app, 5-6 months later reinstall it, it automatically logs me in-- and I was like "Is Google tracking me?" But looks like its Apple's fault. I would have though deleting an app got rid of all its data (like iOS so clearly warns), but looks like it doesnt.