Earlier quoted context omitted.
They arent. They need probable cause to arrest just like any other law enforcement. If they just arrest you because you're annoying or fake charges. You can sue them for deprivation of rights.
CBP has no authority to arrest citizens. They would have to be assuming Lander is undocumented and they clearly have no reason to suspect that.
The Trump administration has been routinely embedding other agencies like the FBI in ICE operations:
https://www.nbcnews.com/politics/justice-department/ice-oper...
Impeding federal law enforcement officers is a crime - to which other federal officers (not sure about ICE) have the ability to make an arrest.