yes, you understand correctly. Proximity to water bodies, dryness of the air (cloud cover or lack of it) and other issues definitely matter.

A major factor, however, is the fact that daytime heating is a lot less intense when the sun is a lot lower to the horizon, so the heating is less than it would be if the sun were higher (it isn't only that there is less time of sun exposure, but also that the sun is not even close to as high in the sky).

The local temperature "wants" to be at the median temperature for the location (where it would stay if input and output was the same across the entire 24 hour period). In winter, the amount of heating is a lot less (much less sunlight per unit area), so the increase ABOVE median is smaller, and thus the cooling is equally less severe to get back to median, and the magnitude of variation is smaller.

One cannot ignore the role of atmospheric moisture though. This is a major factor in why cloudless winter nights tend to be so dang cold but cloudy weather isn't generally cold. The clouds and the greenhouse effect of water limit the amount of heat which can make it out into space, so the lower atmosphere stays warmer (loses a lot less heat to space). The flip side, of course, is that cloudiness also reduces the amount of sunlight making it down to the ground and heating things up in daytime. It is definitely a complicated process, many factors matter.