"Industrial sized" usually describes an object or machine that is bigger and more capable than ordinary, built for use in industry or business. A air conditioning unit for a big building could be described as "industrial sized," because it is much larger and more capable than one you would find at a house.
I have never heard of "industrial size" and I am both an industrial engineer and native English speaker. I think the words "grade" for durability, "scale" for number of products "strength" for power or effectiveness are more appropriate and commonly used to distinguish between domestic and industrial products. Of course "commercial or wholesale size" is normal when referring to batch purchasing. Maybe a Spanish speaker can confirm.
Because this sentence does not have a noun, it makes it only a fraction of a sentence, thus making it have no meaning. It is just there as a way to teach you. DL could have put something in there, but knowing them they probably would have put in something in like "madre" or "oso".
It has meaning but Duo has resisted the urge to add a weird noun (on this occasion, at least). Duo seems to like certain nouns above others so in Spanish Duo would have opted for "Fresa", in German "Zeitnung", in French "Robe" and in Polish "Ciasteczka" (Polski Duo does like the cookies).
I was trying to understand what this means. Sometimes I will (jokingly) say something is "Extra-large, industrial size" to describe something. Those really large cans of corn that you can buy from warehouse stores I've always called "institutional-size" because they are usually used for hospitals, schools, or other places where large quantities of food are served.