Not my words, it is exactly what happened, I can't find the tweets/article right now to show the proof.
What basically happened is Chinese came in large numbers, clashes happened on the LAC, but the local ITBP commander did not find it important enough to report it to higher command, but rather tried to handle it himself (probably out of fear of getting rebuked for not able to handle small matters and relying on the army).
When he finally felt like reporting the full picture to the higher command, things were already quite late, and the Chinese has already built up and captured the peaks.
Of course, ITBPs won't be able to handle battalion-size Chinese forces, ITBP's task isn't to face the Chinese, but just to police the border and handle small matters, not full-scale war build-up.
In essence, the ITBP commander's decision of not immediately reporting delayed our response and we let the Chinese get entrenched on F4 ridge.