Dam the yams!!

Can someone help me out and tell me what in the heck this is??
Because I am not sure what we ate for dinner tonight....

I wanted to buy sweet potatoes...but ran into a little problem at the store.
It went down like this...
I reached for what I thought were the sweet potatoes but then realized that the yams and sweet potatoes looked very similar and I really couldn't remember what a sweet potato should look like...
To add to my confusion, I really don't know what a yam is either....

My gut told me to buy the ones on the left...even though they were labeled yams.

But I asked the produce guy and he confirmed that they were labeled correctly and I wanted the ones on the right.

But tonight as soon as I cut into them, I knew something was very wrong...
The inside was not orange like a sweet potato...

So what the heck is this thing????