You're right - I should have specified that the term 'role model' would be a better translation than just the word 'model'; so the full sentence would still include the word 'positive', i.e.: 'He is a positive role model'.
A role model is one who sets examples or an example of a concept, be it good or bad, positive or negative, depending on perspective. But in this exercise, I'm almost certain that the model being referred to is the role-model. For instance, if you really like football and you hope to one day play like David Beckham, David is your role-model.
In English, when we use model without the attachable 'role', we're most likely talking about someone who poses in designer clothes for a living.
However, it's not limited to that, among scientists and other intellectuals, a model simply means an example or blueprint of anything depending on the field of study. For example, to an architect, a model is the miniature manifestation of an intended structure while in an apple lab, a model might be the prototype of a possible iphone, and on.
I'm afraid I have some trouble understand the meaning of this sentence :-\ I can see some interpretation, but I really don't know which one can really fit.
Is he a model to be followed, in a positive way?
Is he someone whose job is to dress new clothes… and does he fit for the particular cloth we are proposing? I've seen some comment about “role model”, but I'm afraid I don't know what a role model is :-\
Or should it be “It is a positive (scientific) model”, a mathematical model that happens to be positive, i.e. correct, with respect to some data?
As you can see, I'm a little lost with this sentence ☹