First, be aware that consumerization is jargon from the field of marketing, so you should not expect it to be understood in general conversation.
You can easily find a definition of consumerization online:
Consumerization is the reorientation of product and service designs to focus on (and market to) the end user as an individual consumer, in contrast with an earlier era of only organization-oriented offerings (designed solely for business-to-business or business-to-government sales).
A classic example of consumerization is the smartphone. In the early 2000's, the dominant player in the phone-with-email market was Blackberry, which was marketed and sold at the organizational level. That is, Blackberry would enter into an agreement with a large company where the company would use Blackberry network and all employees would get identical Blackberry phones. There was no end user choice and the sales relationship was, as your quote says, "the salesperson [at Blackberry]'s relationship with the person on the other side [e.g., the director of the IT department]."
With the invention of the iPhone (and eventually Android phones), the choice of device became more and more consumerized - that is, the person using the phone chose which device they wanted, even if their employer was paying for it. With this increase in consumer choice, it also changed the demand for features and functionality - consumers wanted the ability to customize their home screens or to play games or listen to podcasts or to do all sorts of things on their phone that their employers didn't care about and were not really central to the supposed "core purpose" of a mobile email device. The companies who offered these consumerized features thrived; Blackberry wasn't able to pivot from organizational features like IT control over your device to more consumerized features like on-line app stores, so it lost most of its market.
The article you've linked to seems to be using consumerization in a slightly broader sense (including healthcare and direct-to-customer manufacturing), but in all cases, it's talking about designing a marketing and sales strategy to appeal directly to the consumer without any intermediate layer such as a corporate purchaser or a health provider network or a retail distributor.