I'm sorry about your sweater! I guess on the bright side, it's a lesson learned, right?
To me, "hand washable" translates into "hand wash (and dry) only", which translates into no machine shall touch this, ever.
Felting happens when wool is subjected to temperature changes and/or agitation. If you put it in the dryer after 2 days, I assume it was still wet, and cold. In the dryer it was subjected to heat and agitation (the tumbling), therefore you were treated with a felted sweater.
If your washing machine will wash it gently enough on the hand wash setting, you can do that, so long as you know you are taking a risk. Even on cold, the agitation alone could felt your wool. And well, never, ever dry a wool sweater in the dryer.. that will ALWAYS felt a hand wash wool.