I mean, that probably IS why they were denied. Anyone in arrears more than $2500 receives an initial letter saying to fix it within 90 days, and if they don’t, they get denied. In the state I live in, they don’t release the passport until the full balance is paid off. Other states might make payment plans. The venn diagram of sovcits and people who owe back support has a decent amount of overlap, so it wouldn’t be at all surprising if this person owes.
The Dept of State would normally either send them a regular ass passport, or a letter saying, “Your sovcit nonsense is nonsense, you can either get a regular ass passport, or we’re keeping your money and you get nothing,” but no point in that since this moron is probably not going to pay their past due support anyway.