Your understanding of this is incorrect. For one thing, the extract that says “a player gains control/possession of the ball after it has touches their arm" contains a typo, and has been replaced with a newer version.
Also, the part that says "football expects a player to be penalised for handball..." is not the actual rule, but an explanation of why the rule is being updated. You have to look at the actual rule to see that it is being interpreted incorrectly.
So, with apologies for repeating myself, here again is the actual rule.
The offence is committed when the ball touches the hand or arm of a player, and then that same player gains possession or control of the ball. The ball touched Laporte's arm, but he did not gain control or possession of the ball. Therefore he did not commit the offence. Therefore he should not have been penalised. Therefore it was a goal and we have been robbed of two points.