Running a player through Dragon of Icespire Peak and they found the necklace of fireballs. However, the wording of the item has me a bit confused on how it might work:

This necklace has 1d6 + 3 beads hanging from it. You can use an action to detach a bead and throw it up to 60 feet away. When it reaches the end of its trajectory, the bead detonates as a 3rd-level fireball spell (save DC 15).

You can hurl multiple beads, or even the whole necklace, as one action. When you do so, increase the level of the fireball by 1 for each bead beyond the first.

Let's say the necklace has 4 beads, and the player decides to throw them all at once. Does this mean:

• There's one fireball that's now 6th level (3rd+3 more levels due to the total of 4 beads); or
• There are four fireballs, each of them 6th level due to the total number of beads

You can hurl multiple beads... 

 ... Increase the level of THE fireball...

As written, it looks like one fireball. It's strength can be augmented by using more beads.

Correct. It’s a waste and is almost always better to throw them individually.

Yes, the use of the singular fireball at that point seems to indicate it's a single, augmented fireball.

Weird. I have to assume that was the designers trying to keep the item from being too powerful?

Yep - each bead thrown increases the level of the fireball by one. So two beads is a four level fireball, 3 is 5th level and 4 would be ONE sixth level fireball. It would be a massively overpowered item if throwing 4 beads was equivalent to a simultaneous casting of 4 fireballs doing 32d6 damage ...