I have been in the same boat as I too transitioned from a software development role to IT Sales and Marketing, after a BE in IT.I can say that while working on the technical issues, I was also exposed to the business aspect like client meetings/calls for requirements gathering, business analysis, research etc. This got me interested in understanding the customer and to figure out ways to address a business need/problem. If possible, cite relevant examples, events, meetings to corroborate your story. All this should point out to your interest in marketing is a way to understand customer's requirements and sales as a planned way of actually reaching out to the customer. I want to take a focused approach to understand the nuances of this field which I want to make a career in.