The last comment is definately retail POV, a better way of saying it is a vendor can be many different things, depending on the nature of the business. It could be sales, marketing, or even an elevator repairman. To use another 'Disney' example, a hotel that wants their particular brand recommended to prospective clients will have representatives or 'vendors' at a travel agency like Walt Disney Travel from time to time.
A vendor is not necessarily a salesman or a caterer but are third party company representatives that are tasked to take care of any issues with their employer's products and handle inventory management issues like ordering or returns.
In some instances, especially in the retail setting, a rep from one of a business' suppliers is on site on a regular basis doing work. For example, Walt Disney Studios and most of the major toy makers (to name just a few examples) have reps going to various retail stores servicing their product to insure product placement (everything in retail stores is placed there for a reason and most chains charge for prime product placement) and handling things like stocking, ordering, returns on discontinued items or overstock and the building of displays.
This is just way too funny. I am a legacy troll and the "vendor" arrived for the big kick-off this week as they begin to replace our legacy systems with the new system. Our "vendor" is the company that we bought the new software system from.
A vendor, as it is used in the strip, is a 3rd party business that wants to sell its services or product through Dilberts company. Often the term 'vendor' is used for companies that show up at a jobsite with fliers or snacks for various employees to promote their services. It could also be used to describe a 3rd party that does business on site like a plumber or gardener.