That's still above freezing, which some may not consider "cold".
For example, even 'basic' heat pumps, the ones that look exactly the same as AC-only boxes, can typically work down to 5C. However once you drop down freezing and into the negatives (C) you tend to need mini-split systems. That's what the GP may mean when the word "cold" was used.
* https://www.fujitsugeneral.com/us/residential/what-is-a-mini...
> A single-zone (also called a mini-split) ductless system allows you to control the temperature of one room by connecting an outdoor unit to an indoor unit, with no ductwork needed. An outdoor mini-split unit is placed outside your home and is connected to an indoor mini-split unit by small cables and a refrigerant line through a hole in the wall.
* https://www.trane.com/residential/en/products/ductless-syste...
> A multi-zone (also called a multi-split) ductless system connects an outdoor unit to an one or more indoor units, letting you control the temperature in several different zones of your home. Variable Refrigerant Flow (VRF) systems are a type of multi-zone ductless systems. VRF systems are energy efficient, and they can be used to heat one zone while cooling a different zone at the same time.
* https://www.trane.com/residential/en/products/ductless-syste...
I know that it's not Montana, but the vast majority of people aren't walking around in T-shirts in almost-freezing weather. These temperatures are pretty objectively cold, if you ask me.
FWIW, I've been to SF, but have never lived there. I am from (and currently live in) a much colder city. Even during summers where I've been to SF, I've experienced significant wind chills which have forced me to wear a hoodie.