Concentrated thinking and reflecting can be more or less the same thing depending on what you are using the terms in relationship to. This person said something specific, in order to write about it. I would still need to know what the writing is for. Is it just to make a scholarly presentation, to get famous, for a book and so on?
That would be a different intention for your reflecting or concentrated thinking compared to actually thinking about your Dukkha, how to end it, and how not to have Dukkha come again in the future. It has a lot to do with what your intention is behind those thoughts. Then we would see a a difference between the two as to their purpose, what we are doing it for. But otherwise, as to the English language usage, if we say we are reflecting on Dukkha or doing concentrated thought on Dukkha, that basically means very similar things.