That link is for infrared thermometer readings. Hence, low temperature. It's bizarre how you are surprised by this. Anodization greatly increases the surface roughness of aluminum. This information is easy to find from lots of sources:

Gabrian

Anodized Aluminum Heatsinks: What You Need to Know - Gabrian

Heat sinks act as passive heat exchangers in many electronic devices, and many aluminum heat sinks are anodized. What benefits does anodization offer?