I just bought a new bowl for my one week old first bong but after walking out I realized the joint on it isn't ground glass like the joint on the downstem, it still seems to fit pretty snug but is it bad to put a non ground glass joint on a ground glass joint? I spent a decent amount of money to get a nice looking bowl so I hope I didn't waste it.
It really shouldn't be that big of a deal as long as it's air tight or nearly air tight. You probably should have inspected that though because I've never seen a bowl that didn't have that sanded glass. But yeah you should be fine.
if you have a picture, it would help.... but it sounds like it's probably a hand-ground joint.... unless it has a grommet in which case, I believe they call the grommet/o-ring setups "technical glass" these days. If it's just a hand-ground joint as I suspect, you'll be good with whatever size joint.... even when hand-ground, glassblowers know there are industry standards and will usually blow them for 10mm, 14mm, or 18mm fittings.