I am not a pro referee. I used to referee lower league in my country but I'm retired now, I chose to focus on my off-the-field career. But I will try to explain the best I can.

Penalty kick is undoubtedly the correct decision.

I could not see a bigger picture of the moment the ball is hit, so I'm just assuming the player is nearer to the opponents' goal than the second last opponent.

Is the Antlers player in an offside position? Yes.

Should it be called? No. There is a distinction between being in an offside position and committing an offside offence. Being in an offside position isn't in itself wrong. Laws of the game says a player being in an offside position is committing an offence if one of the following 3 situations apply:

1) He is interfering with play. This means he directly plays the ball passed by a teammate. Obviously not the case here.

2) He is gaining an advantage by being in that position. This is defined by FIFA, because it is obviously ambiguous if you take it at face value. As FIFA says, it refers to the situations where the ball is deflected after a teammate's pass or off the post and the offside player plays the ball. Obviously not the case here.

I've left this one for last since it's really the only remotely debatable one:

3) He is interfering with an opponent. What does that mean? A little bit ambiguous right? No worries, FIFA has got us covered with a definition: "“interfering with an opponent” means preventing an opponent from playing or being able to play the ball by clearly obstructing the opponent’s line of vision or challenging an opponent for the ball". Is the Antlers player challenging the Atletico Nacional player? Not at all, it's the other way around. Is the Antlers player obstructing the Atletico Nacional player's line of vision? Obviously not. The ball is somewhere on the left side, the Colombian player has the back of his head turned towards the Japanese player.