The box 4 amount is Federal tax withholding - the amount that the account trustee sent to the IRS to pay the "estimated" tax on the distribution. No different than W-2 Tax withholding that an employer does.
That withholding will be added to all other W-2 and 1099 withholding on the 1040 line 17 to offset any tax liability.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
