Not sure, but it may be some type of millet. A bird probably pooped out the seeds. If you don't want it all over maybe you should pull it up.

Agree that it is a bird gift but doubt if it's invasive. See what the seed looks like and maybe you'll want to offer it back to the birds.

It sure looks like millet and some nuseries are selling it for an ornamental. My neighbor had one pop up in her yard last year. I wonder if it is from a bird feeder. THere is plenty of millet seed in mixes. By the way, this year it didn't come back, so enjoy

Seems that the general consensus is that birds are the answer and I do have a birdfeeder not too far away. This must be it, thanks!