you're not overreacting, computers aren't supposed to start smoking. you could seriously damage your computer's components if you let it continue. if it happens again, try to take a picture of it.
is your computer properly ventilated? one or two fans for the case cooling should be fine as long as you also have fans on your CPU and GPU, and to be extra careful you want heat spreaders on your ram:

most ram sticks/prebuilt PCs come with heat spreaders when you buy them. mine don't because i bought them secondhand, but my PC doesn't overheat.