Bettas are tropical fish that require tropical temperatures. Any glimpse of a reputable care sheet shows this.
The temperatures for keeping bettas are highly debatable because they depend on where the betta lives and the temperature. During the summer shallow water temps can reach 85 F which is why the betta has a labyrinth organ. However, that is an extreme, and water temps even in the most tropical places can drop to 60 F. The fact that bettas become listless below 75 F is false. I have bettas in two setups one sitting at 70 F and one at 75 F they both act the exact same. My bettas also generally live 2-3X longer than the care sheets call for. Therefore if the room temperature is below 65 F he should use a higher quality heater. Due to the laws of physics the water, unless altered, will stay at ambient temperature.
What people fail to understand is that bettas don't just live in shallow pools, they also live in slow moving streams, which can be cooler then standing water.
If it is at all helpful im saying 65F is an extreme anything below requires a heater, 70-77F is optimal temps, 85F being the other extreme.
water quality is far more of an issue for bettas than temps