The faucet tends to have some sort of control apparatus (maybe a "valve", sometimes festooned by a "knob") to enable the user to interactively choose the amount of water from each pipe that goes into the faucet.

Now, such apparatus might be comprised of two valves, each one for hot and cold water separately, or a single control which may be rotated to select the mixture amount, or an automaic thermostatic apparatus with a target water temperature dial that the operating user may set to a target temperature which may be called "hot" or "cold" and will adjust the water mixture from the hot and cold water pipes accordingly.

OP's picture seems to have been sent in bad faith, but it does include a control apparatus comprised of a valve with a knob, which can be construed as the tenant showing they had done their due diligence in discovering it is by turning the pertaining knob to open the hot water pipe valve, and nothing else, that after a reasonable waiting period, the water coming out of the faucet is indeed still cold and not hot as intended by the expected behavior of the installed mechanism.

If the tenant misled the landlord by showing a tap which had only a single cold water pipe connection, or failed to correctly operate the valves connected to the faucet in order to produce the desired hot water, then the landlord could fairly charge them with any delays or extra charges incurred from being provided with false information, like the cost of sending a plumber to check on the heater... instead of a dog with a stick to bonk the tenant for being an idiot and not turning the right valve to the faucet.