Most evidence points to a Hamas rocket. I posted a "likely Israeli artillery claim" by "experts" on twitter to showcase how fucking dumb it's to use twitter for sourcing. If we scrutinized all the antivax and pro-Russia shit coming out of that cesspool, I don't see why it ought to be different for this conflict. I also don't buy anything coming out of the IDF, Hamas run health authorities, or Western press at large w/o a presence inside Gaza not just relying on hearsay. There's very little in the region that one could consider "impartial".
I don't buy for a second "hundreds" died in a parking lot strike, but I'm as equally suspicious about 40 intentional beheaded infants.