When I worked in telco, if a customer came in knowing what they wanted I would not offer alternatives unless we did not have stock of what they were after. If you do, the moment something goes wrong, the salesperson is immediately the person to blame (in the same way that if you help someone who is computer-illiterate with their PC, everything that goes wrong in the future is because you touched it). Customers will come back, sometimes multiple times a day, to harass you because you 'made them buy this damn phone'. It never happened to me, but I saw it happen to many of my coworkers (especially the few who were happy to talk customers out of an iPhone purchase for an Android one, back in the 2.x days of Android).

He may have been trying to be helpful, but like you said, I suspect it was because they didn't have stock and he wanted to make a sale for his KPIs.