They had both grenades and explosive charges plus weapons picked up from the army base Hamas overran. All of this can do a lot of damage.
You’re channeling misinformation from Max Blumenthal. The following article dissects his lies which have tended to be repeated by those like you who deny Hamas’s culpability for the massacre of Oct 7:
haaretz COM/israel-news/2023-11-27/ty-article-opinion/exposing-max-blumenthals-deceptive-claim-israel-is-responsible-for-most-october-7-victims/0000018c-102f-d65f-a7dd-f0ff7b550000