Is this just a different way to call the same thing, and if not, what differenciates them?
In younger disciplines, such as those embraced by the term User Experience, there seems to be a struggle of what to call things. There is an ongoing battle between Information Architects and Interaction Designers of who “rules the world of User Experience”. One could follow this war of definition in research papers, credible news sources within the world of academia.
From what I've read the same goes for the terms user flow and interaction model. On could be mistaken to think that there could be more than one user flow in an interaction model, but from what I know – this is not the case. A few image searches of both terms give surprisingly similar results. But there are a difference.
Uxmatters.com defines an interaction model in this way:
An interaction model is a design model that binds an application together in a way that supports the conceptual models of its target users. It is the glue that holds an application together. It defines how all of the objects and actions that are part of an application interrelate, in ways that mirror and support real-life user interactions.
… And according to sitepoint.com, User Flows are:
User flows are simple diagrams that follow a user down a path of activity. Occasionally they look like storyboards, other times like flow charts. The important thing is to not outline every single possible behavior, but rather show most likely user experience. It’s a good way to understand what the product does without being confused by every tiny detail. It is particularly useful if one needs to explain the core interactions to someone new or not deeply involved with the project.
As we can read, very similar apart from one thing: all objects. The interaction model defines all objects, and user flows only main paths (flows) of the application. That is the main difference between user flows and interaction model.
Just a warning in the end, labels may have different meaning in different companies. The important thing is that your team all agree what you mean by user flow and interaction model.