Fat composition differs between mammals.
Cow milk != people milk. It’s one reason you can’t really feed human babies on just cow milk and expect them to be healthy.
I had a refrigerator door full of those little breast milk containers when I was pumping for my middle baby. They got a hard shell of fat congealed on the top.
Accidentally left one out overnight and the little shell of fat was still there in the morning. Temp in my house was around 70, it was winter.
Fats are odd chemical mixtures, because the melting temperatures are often significantly higher than the congealing temperatures. Also, room temperature to a scientist is about 25 degrees C, which translates to 77 degrees F—so your house was actually below room temperature, which would slow or inhibit the fat becoming liquid again after being solidified in the fridge.