I cansee why DirtMechanic said 'It looks like some sort of spinach', it looks softer and more herbacious than a blueberry bush, on the other hand that might just be that it is young. The trouble is not only do so many things have leaves a bit like that, it could even be Basil, but weeds also have this amazing knack of growing next to things they look like. I know it is ridiculous, but sometimes you can imagine them thinking 'I'll be able to sneak in here and flower before anyone realises'
I guess the only way you will be sure is to wait and see how it develops. I hope you are lucky.
Whenever I have seen blueberry plants for sale they have always been named varieties, as they like to cross pollinate that suggests propagation is usually directly from another plant, and when I look they suggest cuttings and air layering, but I also found this
"
Place your seeds in damp sphagnum peat in a seed tray, and then cover them with a ½ cm of soil. Keep them consistently damp and in a in a warm, sunny area (16 - 20 C). You won't see any sprouting for six to eight weeks (or even up to 3 months in some cases)."
So how long did it take to show?