It wasn't until the Little Cosmicub's attention inexplicably focused on the other side of the door that he became certain.
A newly born spirit beast is usually more sensitive to external stimuli and easily attracted by novel things and phenomena.
At that time, there were so many things around it.
Several staff members were talking nearby, and the Little Cosmicub was crying in front of it.
According to common sense, its attention should not have been drawn to the outside of the door.
Unless something outside the door caught its attention.
Assuming the Little Cosmicub is a spirit beast with psychic-type abilities, then all its actions would be reasonable.
Its psychic abilities allowed it to sense the commotion outside the door.
It's just being born and using this ability for the first time, it naturally became curious about the noise outside.