Dolphins giving false lead

I noticed dolphins seem to point where there is no treasure.

I encountered this in world seed 1, at the underwater ruin close to spawn. When fed, dolphins go to a point just about coordinates 60, 50, 70. But there is no chest there.

I tried going to spectator mode, but no chests are close at all.

I found and removed two chest from dungeons nearby, to see if they were causing the dolphins to point there, but no change. 

To reproduce: Create a new world with seed 1 in creative, go to coordinates 60, 50, 70. Notice underwater ruin. Find or spawn a dolphin, feed it cod. Observe dolphin.

Expected result: Dolphin will point toward nearest chest, trailing white stars.

Observed result: Dolphin will swim till 60, 50, 70, trsiling white stars. No chests are nearby.