Although Goldy was still far from being an actual Golden Crow, he already possessed some of its qualities. In addition to that, Goldy was already near the point of evolution, so the stimulation it received from the divine lightning was the pivotal moment when he broke through to Rank 4.
Goldy didn't have a blood contract owner and he wasn't a monster either. Instead, he possessed the bloodline of a legendary beast. Statistically speaking he was a Rank 4, but thanks to his unique bloodline, his true strength was comparable to a Rank 5 beast, maybe even stronger.
This was why Lin Jin had the confidence to march right up to Daluo Temple.
Upon witnessing this intimidating display, the monks froze up in fear. While they had already noticed how unusual this rooster was earlier, they did not expect it to be so strong.