dont believe everything you read on the internet 
^^ doesnt make any sense to me.
I’d say ID and PD are pretty much interchangeable at this point, both in and out of the industry. Both refer to the design of products for functional use. Volume of production not being so relevant in my opinion as purpose. That being said, the function/object can vary from anything including play (toys) to “play” (s3x toys), and everything in between.
Im in footwear now, but previously, I used to say the following about ID-
“Architects design buildings. Industrial Designers designer everything else.”
- pretty much covers it at least as a general response to “what is ID”. Of course engineers might take issue (re: bridge designs, motors, etc. but for the most part is pretty accurate).
R