Distributions are a proportionate mix of basis and pre-tax amounts. If less than your entire basis is being applied when determining the taxable amount, it implies that you did not have a zero balance in traditional IRAs at the end of 2025.
Knowing that the taxable amount is $2,400 says nothing about the amount of the distribution, the amount of the year-end balance, or the amount of basis being applied to the distribution. You can view the calculation of the taxable amounts on Form 8606 Part I and if TurboTax puts asterisks on lines 13 and 15, on the Taxable IRA Distribution Worksheet.
