Well this is what happened and they didn't lose any lifepoints for it
Though it states
"If you do not Xyz Summon this turn after Summoning those 3 monsters, you lose 4000 Life Points during the End Phase."
Turn 1:
Premature Burial on Morphing Jar
Dragon's Ravine to send Blue-Eyes White Dragon and Lightpulsar Dragon to the graveyard
Used Lightpulsar to send 1 Mirage Dragon and 1 Evilswarm Zahak to the graveyard
Activated Maxx "C"
Used Message in a Bottle to summon Maxx "C"with Evilswarm Zahak, and Blue-Eyes White Dragon. Following that they tributed Blue-Eyes and Maxx "C" to summon Darklord Zerato.
Nothing happened
Can you please post a replay.

Because the way you stated it cannot occur.

You said that they used Lightpulsar to send Mirage and Zahak to the grave. This would be a special summon and you cannot special summon except by Xyz during the turn you want to use Message in a bottle.

Also you stated Turn 1 and by Turn 1 they could not have all those cards in a normal duel unless you changed the draw setting before hand.

Anyway I tested this myself, with different cards, and it takes away the 4000 life points just fine.

So if you could please post a replay of this not actually occurring that would be great.

Actually I don't have a replay, because I forgot. But that's what I'm trying to figure out. The only other thing I remember is that it was vs AI
Edit: Okay, so I was able to use different cards and it seemed normal this time with losing the life points. Not sure why the first time didn't happen during the first time.
I was trying things out with a friend and I guess it was just a one time glitch or something