When you have a scoreboard that tracks whenever a particular item is dropped, it both increments for when you drop that item (as expected) but also for when you use the /give command to give the player that item.

For example:

/scoreboard objectives add EggDrop stat.drop.minecraft:spawn_egg

Then upon doing...

/give @p spawn_egg

... the 'EggDrop' scoreboard increments by 1.

I have tested this with a few other specific items and the same problem occurs.
However for dropping items in general, using stat.drop works as intended, so it's just for dropping specific items. I'm also aware that this same problem happened with the 'stat.drop' when that stat was first released, so I expect it's the same kind of problem here.