What cadore said.
Anyone with earned income can make a contribution to a traditional IRA. However, deductibility of traditional IRA contributions phases out with income (as does the ability to make Roth contributions). But the law permits higher earners to convert a traditional IRA to a Roth - the "backdoor Roth." This is a common reason someone might make a non-deductible traditional IRA contribution. However, conversion is usually done immediately after the contribution (there's no required waiting period), so non-deductible contributions from prior years would usually not be in the traditional IRA account anymore. TurboTax is not clear on this point in its instructions: you should only report past-year non-deductible contributions IF THEY ARE STILL IN THE ACCOUNT at the end of the current tax year. Note that mixing of deductible and non-deductible contributions is a little more complicated, as they can't be unmixed (and indeed is the reason for this question in TurboTax).
