I know it’s not the Temple. But Shiloh was where the “proto-temple” Tabernacle was parked for a significant amount of time. The furnishings of the Tabernacle were never of stone.
This wasn’t the Tabernacle altar. It was in front of where the Tabernacle stood.
There are references to indicate a stone altar was used at festivals and such because it was larger and not enclosed in order to accommodate much larger number of sacrifices.
The ‘horns’ were probably originally used to tie animals to, and breaking such horns ruined such altars. A number of these horned stoned altars have been found.