Animals are more intune with certain aspects about humans, than even humans are aware of. These cats here, I am certain, are the same to a certain degree. They are highly sensitive to nervousness in a human, and can interpret it as a threat. At the same time, I believe they can also sense strength, and also interpret that as a threat.

[ He turns his head to "face" Saitama. ]

Maybe it is your strength. Maybe it is your tension.

But whichever it is, not an abnormal reaction.