Let's see. You are heating so you have hot coils inside and the coils outside are cold. It is humid as evidenced by fog. The outdoor coil temperature will be below the dew point of the air. Water will condense and might freeze. Whether or not it freezes, you should expect have dripping.

That make sense, thanks a ton for the reply. I was worried for a while that I had a leak somewhere. New to heat pumps!

This is what heat pumps do when they defrost.

Frost accumulates.

Heavily frosted, defrost begins.

Melting.

Melting and "steaming" (water vapor / evaporation).

Finished.

The system switches to cooling mode during defrost so the outdoor coils heat up (same as during summer cooling operation). The electric "backup/emergency" heat strips in the indoor air handler activate to counteract the cold air that otherwise would be blowing out of the registers.

The outdoor fan shuts off during defrost to concentrate the heat in the coils. The fan turns back on when defrost is finished and the system switches back to heating mode, and a puff of moisture may blow out depending on ambient weather conditions.