The place you went to last year should have entered the amount from box 2a as the taxable amount, so answer "yes" and take the 2016 back to them to Amend as you overpaid your taxes in 2016.
They are incorrect.
The 2 means you are retired below 59 1/2 and have an exception from the penalty for withdrawing prior to 59 1/2.
You paid into your plan with money that did not reduce your taxes and now are recovering some of that money, and that is why it is not taxed and box 2a is smaller than box 1 of the 1099R.
