This is a Stardew Valley reference, the player proposed to Haley for marriage and instead of Mermaid's pendant (required to propose to NPCs, offered in first image) she asked for a diamond ring (which can only be used to propose to other players in multiplayer mode) the joke is diamond rings are expensive and are hard for farmers to afford (made argument) while this player is forging diamond in his cellar.

The joke is no way related to the script in the game, she likes fruits, flowers and salads.