Błędnie: No matter what happened, he appeared to be calm and collective, which proved really uplifting.
Poprawnie: No matter what happened, he appeared to be calm and collected, which was really uplifting.
"Collective" to 'zbiorowy', 'kolektywny'; "collected"- 'opanowany', 'skupiony'. Wyrażenie "calm, (cool) and collected" oznacza 'spokojnego i opanowanego'.