I'm guessing they may not have updated calendars yet for whatever reason. I know ice cream/popcorn/drink carts only was definitely an After Hours party thing, not
MNSSHP. Not sure about the table service restaurants, but a number of the quick service places were open and selling the special party exclusive snacks during MNSSHP.
Though now that I'm thinking about it, I think a lot of quick service places were also open during After Hours parties for exclusive snacks, the only reason ice cream/drink carts were notable at those parties was that they were free.
In conclusion

... I'm going to guess their calendars need updating, or they might not include their party hours at all to avoid confusing day guests so they won't think they can hang out at Cosmic Ray's til midnight.