Yes, armour roll is made by opponent, but where it is said that roller is the person who decide to add +1? Actually bomb is not Mighty Blow (even I used that term), it is: "You may apply a +1 modifier...".
I found discussion about bombardier fumbling:
https://www.reddit.com/r/bloodbowl/comm ... ghty_blow/
And most think decision is made by Coach of Bombardier:
"Bombadier awards the decision of adding +1 to "you", referring to the coach who controls the player that is using the Bombadier skill."
"You choose. The skill states it is your choice. Nothing about bombadier gives that choice to your opponent, like Animal Savagery does."
"The optional +1 for bombadier is awarded to "you", which is the player with the skill. If he blows himself up, you may choose not to apply the modifier."
But there is also opposite view:
"It does in fact say "may" choose to apply it and so it is your opponents call"
And another with bomb exploding:
https://fumbbl.com/index.php?name=PNphp ... ic&t=31726
"This means when you hit your own player you do not add mighty blow, when you hit an opposing player you do add mighty blow "
VS
"I still interpret the "you" in this case as the person rolling the armor and injury dice."
(And after these there will come my question: will this change if bomb is catch and thrown back)