I don't see it. He's talking about bad people (in a concerningly dehumanizing way), and you're just assuming he means all Mexicans.
Well, the Mexicans certainly saw it that way.
But I'll also point out that he
didn't start by clarifying he only wanted to stop "bad people". Reprinting the statement in question:
We have people coming into the country, or trying to come in, and we’re stopping a lot of them, but we’re taking people out of the country.
"people coming into the country" is just immigrants in general. "trying to come in" is still just immigrants in general. But then he says "we’re stopping a lot of them" which strongly implies border control: and in America that's almost entirely blocking Mexicans/Latinos at the border. He's
not talking about Chinese Visa over-stayers or something here. Nobody would interpret it that way. Then, "we’re taking people out of the country" this is a reference to deportation. While it's possible he means here "deportation in general" it's fairly clear that the subtext is deported Mexican/Latinos, especially since he already referred to blocking this group of people from getting in.
e.g the first part is the part that
defines which group he's talking about. He then says
of that group:
You wouldn’t believe how bad these people are.
e.g. he
already defined who he's talking about, and now he's
saying they're bad. He's not
only talking about "bad people" as the object in this statement, because that would be circular logic. e.g. that would be like saying if you define a "group X" then say "you wouldn't believe how evil X are" you're
only referring to "evil Xs" rather than stating that "all Xs are evil". Which just plain wouldn't make sense.
e.g.
sure Trump could have only meant
specific people he's trying to stop, but if we e.g. remove completely the "Mexicans" assumption I made, then it looks even worse. He's just defining a group we normally call "immigrants" in general, then saying you wouldn't believe how bad they are, they're animals. Really good optics.