Mystery plant(s)

This year was my first attempt at companion planting. Also known as "put plants that play well together next to each other". Now, I'm still learning about gardening in general so I'm figuring all of this out as I go. I read that green onions and carrots are great planted together since the onions have very shallow roots and tend to keep some bugs away and the carrots obviously go much deeper. So I cheerfully sowed a bunch of carrot seed and then a bunch of green onion seed and waited for them to grow.

Here's the rub. Did I mention that I'm a bit new to gardening? I didn't know what green onion sprouts looked like. So when a bunch of thin green sprouts came up, all was well. Or so I thought. But now I'm staring at a thicket of something that is definitely not onion of any sort. Whatever it is, it's growing like a weed, but it can't be a weed since it did come from one of my seed packets. Just not the green onion packet. I did have some flower seeds, but I don't recognize these at all.

Anyone want to venture a guess?