Three wires actually. Here's the install guide: Electric Vehicle Charging Station EV230WS–Installation
, the guide notes, "NOTE: Use AWG 8 copper or aluminum wire rated 90 degrees C or higher." If I was going to hardwire it as they suggest, I'd use a flex conduit from the existing box. Remove the receptacle and replace with a metal plate for the conduit.
Other makers (Blink and SPX) have supplied NEMA 6-50 pigtails and used a receptacle. My Blink is installed that way, and it's been handy to be able to power off the unit by unplugging without going out to the service panel and flipping the breaker. If it were my unit, I wouldn't hesitate to use either a 6-50 pigtail or simply buy a heavy appliance cord
for the 14-50 receptacle you already have. Keep the pigtail nice and short, Just long enough to reach the outlet. Depending on circumstance, you may find you have to rotate the receptacle to accommodate the plug.
Edit:Taking a better look at the install guide, it looks like you'd run the pigtail out the top of the unit, and assuming the unit is mounted next to the outlet, the plug would be the correct orientation for your "upside-down" receptacle.