Being a "climate change denier" can mean almost anything today.

Such as that you believe that climate is changing not because of CO2 levels but rather due to other atmospheric gases or pollutants, or the sun's emissions, etc.

Or maybe you believe that the models being used are politically driven (which is a provable fact BTW).

You can still agree that there is a problem, but you just don't agree on the causes 100% or the solutions 100%.

So unless you know the specifics of what this person is not agreeing with you on, it is a meaningless and non-relevant label.