iterators have this thing called taboos, rules written into every single of their cells preventing them from doing things the ancients wouldn't want them to (hurting their creators, self-destructing, etc). some iterators (i think they were called sliverists, though i might be wrong), suns and pebbles included, were very into the idea of finding a way to self-destruct.
suns had an idea, but since not ALL iterators liked the thought of breaking taboos and stuff, they sent it through a pearl instead of risking being overheard on broadcast.
their plan was to carefully rewrite every cell's genome. the command had to be very specific, overriding the taboo you want to break but doing absolutely nothing else. this would require a lot of time and focus unless you ran a lot of parallel processes and consumed a hell ton of water. and then you know what happens
the forced interruption likely caused pebbles to do something wrong in a panic. (though i'm not 100% sure about this part. all he says is "you could not have chosen a worse moment to disturb me")
if you want to know the specific details (or check if i'm actually telling the truth because i might be wrong about some things) you can just... read the pearl page on the wiki. you can find a lot of lore there https://rainworld.miraheze.org/wiki/Pearl/Dialogue