It's a bit of a marketing ploy. Not on this guy selling, he's repeating what he is seeing.
The class is technically semi professional (the semi industrial comes more from sellers of the machines rather then the brand itself) and has been around since at least the 1930s in advertisements (which could be earlier, but I noticed it in the ads for Singer 201s consistently starting in 1938). It also has appeared as dressmaker/tailor machines in ads promoting sewing from home as a business in middle 20th century as well.
Modernly, these machines are kind of all over the place and nothing is the same from brand or model. It can include any or all of these: the ability to use industrial folders/feet (aka high shank), a larger harp area, all metal/mostly metal, can sew faster then a domestic by usually twice the speed (1500-2000 SPM) which is the most consistent feature of this category, straight stitch only and may have special feet that industrial machines don't offer but are model specific making the machine more usable in domestic applications then just an industrial, be gear driven like industrial machines...the list actually goes on fairly long on what they can do.
But even industrial machines aren't made for heavy items consistently. My industrial has to have a needle plate, feed dog, foot, stitch regulator, hook and needle bar changed out to sew really heavy fabrics and is geared for light to medium-heavy weight fabrics. Most denim can be sewn on the machine for alterations (up to 13 oz, depending on brand and content with the majority sold today being under 12 oz...denim is all really light now), but at about 15 oz denim and heavier fabrics (and I sew 18-22 oz denim and vinyl and canvas) I use a different industrial that has a larger presser foot clearance, harp and was originally meant to sew saddles since even industrials aren't made equal.