The most reasonable conclusion the student can draw is:
The electrostatic forces between molecules in the unknown liquid are stronger than the electrostatic forces between water molecules.
This is because the unknown liquid has a higher melting point than water, suggesting that the intermolecular forces (such as hydrogen bonding, dipole-dipole interactions, or London dispersion forces) in the unknown liquid are stronger than those in water, which is why it requires a higher temperature to transition into a liquid state.