i think for sure they want to redo or do further medical tests.You might passed them in border line for example say blood pressure should be around 140/80 (Approx guessing its not actual) you might just passed in border.they want to re confirm.
don't worry it will be simple tests.
it happened same with my friend he passed his BP just in border line cic asked him to do additional test like creatine blood test and ECG.
They asked him to use some medicines and thats it he got cleared his medicals.
I just shared my experience. it might be different for case to case.