He is right and you are wrong
Splitpushing works also as a game strategy on his own... it CAN be used as a distraction, but it is not automatically it, you can use to purposedly win the game
Your objective is to take down nexus, and to do this you got to take down lane turrets, than inhibs, than nexus turrets, and then nexus, the strategy to do it doesn't really matter
Win team fights is a way to have a free time window to take down turrets, but you don't have to necessarily take down turrets this way.
You can sneak unnoticed on a lane and push tower down, and that's what splitpushing in.
You can draw attention to you while splitpushing free the map for your team to take objectives...when you splitpush you are not automatically the distraction, you can be the main threat enemies have to fight, and the team can use the fact you draw attention to keep up in farm or do something else
Call it a mere distraction is silly, because you can use the splitpushing strategy in many different way...
Example:
Past lane phase, your teams is losing fights in a game, the enemy group and take mid inhib and while you are forced to defend against minion wave, they go back to then take an objective like a dragon/baron. You can't literaly reverse the push direction in mid lane by the time they take the uncontested objective.
How can you try to win the game? While the enemy is taking an objective and your team is defending, you can go on a side lane, take a tower down, and open a way for the enemy inhib-> nexus if you win next figth or for a backdoor/base race
Here the splitpushing is not a distraction to allow your team to do something, it is a way to trade some objective while the enemy get theirselves an objective getting a big advantage and try to not get too far behind and build a possible way to success