It is true though. The climate has been both warmer and colder than it is now just several centuries ago (little ice age, medieval warm period). This is well documented and accepted by scientists even though reasons are not clear (definitely not human activity at that time obviously).

In our current era humans are contributing to the changing climate in a very big way given our industrialization, the extreme levels of population and economy dependent on extracting oil and coal from the ground and burning it. That does not change the fact that climate has been changing even before humans could have any noticeable impact on it, and those changes were often very fast and sometimes cyclical.