Small fireballs disappear harmlessly when hitting an end crystal. This happens regardless of /gamerule mob_griefing and regardless of whether the small fireball has an Owner. For comparison, skeleton arrows and snow golem snowballs detonate end crystals regardless of /gamerule mob_griefing.
To reproduce
Find or place and end crystal in an open area
/execute at @n[type=minecraft:end_crystal] run summon minecraft:small_fireball ~-5 ~1 ~ {Motion:[0.5d,0d,0d]}
❌ The small fireball does not detonate the end crystal
Expected behavior
The small fireball would detonate the end crystal
Note
I understand why this would happen for dragon fireballs, but not small ones. Care should be taken to fix this in a way that prevents dragon fireball behavior from changing.
Can confirm