End Crystals are unaffected by the mobGriefing game rule, doing damage to blocks even with said game rule disabled. This behavior seems out of place considering it's the only entity besides TNT(which serves no other purpose than destroying blocks) that does block damage during direct player interaction with the game rule disabled.

Edit: I tested this interaction in Bedrock Edition, the End Crystal does not damage blocks in that version when the game rule is disabled. This reassures me in believing that this behavior is unintentional.

To reproduce:
-Create a world, preferrably with commands enabled
-Summon or locate an End Crystal
-Use /gamerule mobGriefing false
-Place blocks that can be blown up nearby
-Hit the crystal
-The nearby blocks get destroyed

(Fixed typo)