Federal tax went DOWN after entering wife's foreign embassy income?

Hi, my wife and I are married, filing jointly. My wife is a lawful US permanent resident working for a foreign embassy. I filled out my portion which was pretty straightforward (US citizen working for a US company) and saw that I owed federal tax. After I entered information for my wife's work as outlined here (https://ttlc.intuit.com/community/tax-credits-deductions/discussion/re-my-wife-works-for-a-foreign-g...) I noticed that the total amount owed went DOWN. First off, are the steps outlined in that link correct (I've never entered an amount as negative in TT before) and secondly, why would this result in owing less federal tax?