I think the idea is that, instead of passing across the border in a controlled fashion, to a safe location, they were forced to head to shore to an unsecure location. Strand said the reason they stopped firing was because they figured whatever was on land, would kill them. So they were escaping into a red zone, and the border patrol figured they'd let the red zone take care of them instead of risk their men chasing them.

 

Don't forget that the pirate plot was teased in episode 1 didn't start until episode 4.

I think the pirate plot and the Mexican military plot will eventually dovetail into the Cecila cult plot-line.

 

It was lame writing. Several weeks of build up to nothing. A recurring pattern on the is show. It seems unlikely a military would have let a prize like the Abigail go.

 

Trump didn't have time to build the wall?

 

This was terrible writing. As others have already mentioned, this is the point that this whole season has been building up to. Getting into Mexico was the primary plot point of the season so far, and it got summed up in two minutes. I still don't even really get why any gunfire was exchanged. All we know is "someone said asshole in Spanish" which really doesn't tell us anything. What was actually going on there? Why were they just allowed to leave? Yes, it was said that they assumed they'd be killed by whatever was on land, but this whole huge plot point was just glazed over and given no attention. The entry into Mexico was incredibly anticlimactic.

 

Getting into Mexico has never been the problem, or not a very serious one.
It's getting from Mexico back to the USA where the real hassle begins.
I think people often forget this minute detail, they tend to assume 'crossing the border' means either way.
It's not true, going south is easy, it's the trek north that's arduous.