Distributions from an IRA such as these, regardless of how the money came to be in the IRA, are taxable as ordinary income. They do not get capital gains treatment. The taxable amount of the distribution (the entire amount if you have no after-tax basis in traditional IRAs, which is likely in this case since the traditional IRA is a rollover from a 401(k)) is includible on Form 1040-NR line 4b. If you were under age 59½ at the time of the distribution, the distribution is also subject to a 10% early-distribution penalty unless you have a penalty exception that applies.
