Using deadly force in self defense against law enforcement officer is only justified when that law enforcement officer is acting outside the bounds of the law. The fact that said law enforcement officer had a drawn firearm does not make it legal to shoot that officer. The officers having their firearms drawn was also reasonable given that the rioters were armed with guns. These officers were making a legal arrest, and thus any claim of self defense by the rioters is moot.
Like it or not, ICE is still law enforcement. You don't get to just say "I don't like this agency, so I am justified in gunning down any member of that agency that tries to arrest me."