I feel like a wizard casting Minor Illusion to block the light of a campfire from an enemy patrol is an engaging and creative use of the spell. I would ultimately say that it's up to you to decide where to draw the line, but that the rules state this is nothing but an illusion an...
The bead is likely contained within that 5' minor illusion, but the path it takes to get there can still be seen. This applies whether you took the action to create the Minor Illusion before or after you cast the Delayed Blast Fireball. If no one was there to witness the casting...