Entity Reference get nodes based on tags
It can't be done with Entity Reference out of the box, your only option is to install another module or write some custom code (you would need to create a custom widget that searched additional fields on the entity if you went down the custom code route).  

One possibility, which seems to be in keeping with your approach, is the Entity Reference View Widget module.  This module allows you to search on any field.  There is a little bit of additional setup since you have to create a view containing your Article nodes, but it means that you can specify your taxonomy as a field that can be filtered.