Neither an astrophysics. I skimmed the paper. IIUC the collision with the planet mixed internal layers of the Sun and a lot of the Lithium went to the core and got fussed with Hydrogen.

PS: The paper says that that actual A(Li)=1.1 instead of the expected A(Li)=3.3. I needed a lot of search to understand it until Gemini kindly liked this page. https://astronomy.stackexchange.com/questions/61814/what-do-...

A(Li)=1.1 means the Li/H ratio is 10^(-10.9) = 10^(-8.9)%

A(Li)=3.3 means the Li/H ratio is 10^(-9.7) = 10^(-7.7)%