...my quinoa seedlings!
I can't find a good picture or description online, but I did find a site that said they resemble lamb's quarters, and a picture of lamb's quarters seedlings looks like what I pulled out. I only pulled it out after finding a similar seedling in an entirely separate part of the garden and figuring that then it couldn't possibly be quinoa. I stupidly forgot that dd helped me plant the quinoa and was "putting extra seed out for the birds"
Here's the "help" part: Does anyone know if quinoa seedlings have fuzzy leaves? (I've never grown it before.)