Why is my Fed tax refund larger than TurboTax computed?

Filed 2022 Fed tax before April 18 & received refund early May but Fed refund was about $10 more than Turbo Tax computed.  As of now, why have I not received any IRS letter, explaining why I got a bigger refund???  (I live in CA disaster area & Fed extended filing deadline to Oct 2023 but I was ready to use Turbo Tax to file before April 18, 2023.)