One golem was immune to all magic, the other was immune to all physical attacks. Being noticed by them to cross the red line on the floor made them immediately attack. To be honest, when I was planning that encounter I suspected (and hoped) they would fight, but that was never required. They could have become invisible to try sneaking, they could have used Dispel Magic to at least temporarily disable the golems. There's always options. But combat is fun too and when the group started dilly-dallying Tesaya lost it and went in.