The Arabic word which is used for (cast) is used for a material thing and not for a non-material as the terror.  But Allah (swt), used this word to rest the Companions of the Prophet (saws) after the losses that occurred in the Battle of Uhud, as if to say to them: I will gather terror from all directions and cast it into the hearts of the polytheists.

بِمَا أَشْرَكُواْ بِاللّهِ مَا لَمْ يُنَزِّلْ بِهِ سُلْطَانًا {for what they have associated with Allah of which He had not sent down [any] authority.}: The authority is either the authority of power, or the authority of argument, evidence, and proof, so they do not have authority which is the evidence, to prove their association with Allah (swt), and they will remain in fear until Allah (swt) inherits the earth. Associating partners with Allah (swt) means to believe there are those who harm, benefit, give, prevent, connect, cut, lower, lift, dignify, humiliate, give life and death other than Allah (swt).

{وَبِئْسَ مَثْوَى الظَّالِمِينَ} {and wretched is the residence of the wrongdoers.}:

They are the wrongdoers because they are severely unjust to themselves, that is because they present themselves a quick, temporary favour, as such when a person despises, lies, bribes, and does evil, then he is giving himself a quick favour that ends while he remains in the deprivation of disobedience until he reaches the Fire, so he is unjust to himself and to others at the same time.