If its been in storage all winter its pretty normal. The seals that hold oil in the oil bath get weak over time and let oil past. Then when you start it, it all blows out. The fact you started it w/o having to drain oil out of the motors tells us it isnt that bad.
Now for the enviroment...well thats up to you. I warn people what is happening, but most people just wanna run it till it blows vs. spending big dough having the crank taken apart to replace the seals. I've seen some bad ones too...ones that we had to pump oil out, then use starting fluid just to get it to pop off and blow the oil out.
My Theory on this outside of weak seals is the oil tank has a check valve on it that allows 2-3psi build up from temp changes before it will open. My guess is that pressure pushes oil past the seals.
I left the oil tank lid cracked open on my GFs 93 GTX this winter...in a month I will get to see if my theory was right.