If it was only his nascent soul realm body then that petal would have been enough for him to consume as any more than that would have caused him an explosion.
Fortunately, he also had the Semi God body in him as well, making him incredibly stronger than a normal cultivator, also the unique yin and yang cultivation along with the ancient phoenix mediator inside of him had made him incredibly strong and therefore, had no problem in consuming the celestial tier flowers.
His body had been built differently and was able to take it all in.
The ancient mediator inside Yichen was too widely awakened as it had found something interesting to refine again.
It immediately sped up the refining process and was constantly spreading all the essence to Yichen's entire body.
Now that Yichen saw no harm in him as his ancient mediator was busy helping him out, refining it all, he was then left busy constantly devouring the celestial tier flowers, one after another.