Gift Taxes

A friend of mine's dad passed away in 2021. His dad did not leave a will. His mom gifted him his dad's former truck. The truck had a book value of $21,000 and he sold the truck for $21,000.  Since his mom does not work and had no money, he gave her the $21,000 to pay off the unpaid bills that were left after the father's passing. His mom also gifted him and his younger brother the house. What are the tax consquences for him in 2021? I realize the that $15,000 in annual gifts is not taxable. Thanks in advance.