Obviously not. But the fact that they were crossing illegally in the first place is reasonable suspicion of the possibility that it was not their first offense.
And anyway, the point is: you made the blanket assertion that crossing the border illegally is a misdemeanor - without the qualifier of first offense only.
Actually you are wrong. A subsequent offence is not automatically prosecuted as a felony. It is up to the discretion of the prosecutor's office.
Obviously not. But the fact that they were crossing illegally in the first place is reasonable suspicion of the possibility that it was not their first offense.
Actually, it isn't. "Reasonable suspicion" extends only to the specific act in question. Otherwise, one could detain anyone on any grounds whatsoever--if you make enough leaps of logic, you will magically have "reasonable suspicion" of SOME felony, SOMEWHERE.
Again, please note: they did not actually SEE the crossing event, they only SUSPECTED that these people were crossing the border. It was not an established fact at that point.
And anyway, the point is: you made the blanket assertion that crossing the border illegally is a misdemeanor - without the qualifier of first offense only.
I said "in and of itself." The things that make it a felony are qualifications on the basic charge that must be established as fact prior to making a citizen's arrest.