True, the Mexican Government is assisting Central American invaders.
But there are plenty of Mexican invaders too.
My point is that even though not all the migrants aren’t Mexicans, the Mexican Government are actively assisting them in illegally entering the US.
I don’t know about actively assisting as they aren’t hoisting them over the walls/fences or digging the tunnels under the walls/fences or giving the green light to wade across the Rio Grande, but they are apparently allowing passage through their country.