Hi! The first boss is supposed to be defeated unarmed, and you receive the Hookshot as a reward for doing so. If you're still interested in checking the game out later, I recommend checking out where those platforms on the first boss' both sides lead, they hint at the way you're supposed to defeat it.
But whatever is the case, it's possible that the boss is still too vague an encounter, especially so early on. We could try and mitigate it by marking the first core upgrade (the Hookshot) on the player's map, so that the player can clearly see it's just a few rooms away right after the boss room. Thank you very much for bringing this issue to our attention!