I just looked up the definition:
"[...] a place in which large numbers of people, especially political prisoners or members of persecuted minorities, are deliberately imprisoned in a relatively small area with inadequate facilities, sometimes to provide forced labor or to await mass execution.[..]"
First of all, border crossers are neither a political class nor a persecuted minority (again, another abused nebulous term that means different things to different people). E.g. I'm a white male, and I happen to be a minority where I live. This place even has laws specifically designed to target us, yet here we're supposedly a "ruling minority" or something. Definitely not the same meaning geographically, but even more so politically.
Second. They're not forced to provide manual labor. Best I can tell is that it's voluntary, comparable to existing detention centers for citizens and they get some token pay in return.
Third. They're not there to await mass execution. At this point, using "concentration camp" in the normal "this is a bad thing to do to people" sense is quite hyperbolic. They're there waiting for court and/or deportation. I mean, what else do you want ICE to do if that is their current legal obligation to do? Must they say "screw it, the humane beds/cells are full, let's let those guys run right past us."
I think the above is from the Oxford dictionary according to Google.
Here is the definition from Merriam Webster, too:
"a place where large numbers of people (such as prisoners of war, political prisoners, refugees, or the members of an ethnic or religious minority) are detained or confined under armed guard —used especially in reference to camps created by the Nazis in World War II for the internment and persecution of Jews and other prisoners"