Indians walked themselves into trouble.
For a long period of time, China has endured India's intrusion. And Indians have wrong expectation this will be the same as Doklam.
Before attacking, China called for de-engagement. But China knew India will intrude again. While soldiers pulled back, some infrastructure constructions were still running well within China's LAC.
Meanwhile a a company probably from elite forces/recon unit were waiting for Indians to intrude. They were prepared.
Then an Indian regular regiment commanded by a colonel did intrude and attacked the workers.
Suddenly hell broke loose and Indians lost the streetfight.