Apparently there’s been some confusion (to put it nicely) over what was legitimate and what was fan theory.
This is what we have regarding a recent preview: http://www.narutoforums.com/showpost.php?p=53839223&postcount=582 (Thanks, majin-lu for finding that on 2ch)
Boruto throws Himawari’s birthday cake, and we see Hinata sad about this. It does not specifically say that he throws the cake on anyone, and there is no mention of candles.
These spoilers also mention Naruto being busy as usual and Boruto getting angry saying “But he promised he would come home soon…”
There was also this, which was seperate: http://www.narutoforums.com/showpost.php?p=53839375&postcount=596
It says “It looks like Hinata and Sakura were the only moms in the preview. Hinata with a sad face because of the cake, and Sakura using medical ninjutsu.”
It looks to me like the one who wrote this just wanted to point out what Hinata and Sakura were doing in the preview. It does not necessarily mean that these things happened in the same scene.
The thing about Sakura healing Hinata and Himawari after they had a cake with lit candles thrown on them is completely made up. An NF user was attempting to connect all of the different spoilers together, and I’m pretty sure that this theory was intended as a joke to begin with. Don’t take it seriously.