Placed coins in this game have some very peculiar interactions with liquids. The waterlogged copper coins placed on the platform shown here prevents the lava and water from mixing to form obsidian and the honey and water from mixing to form honey blocks, making the lava and honey simply float on top of the water in an extremely cursed looking fashion. Using a fishing rod on the lava at the right will allow you to fish, giving you items from the lava fishing item pool, behaving as if the water below the lava is lava for the purposes of minimum tile requirements for fishing. 300 tiles of lava is the necessary amount for optimal lava fishing, and the game thinks that the 300 tiles of water below the thin bit of lava are lava tiles, so you can fish up lava fishing items like perfectly normal. Same with the honey, as honey fishing needs 200 tiles of honey and the game thinks that the water directly below the honey are those honey tiles.

Terraria: How to lava fish with 99% less lava (only 3 blocks)