This is definitely most, certainly not the case. I'll explain to you why:

A = set of top 5 disease killers in the U.S (hypertension, obesity, cancer, diabetes, etc)

B = set of corona deaths in the U.S

The intersection between B and A is over 90% of set B's numbers. So basic counting shows that in order to get the proper amount of deaths you'd have to perform the following calculation of:

A + B - ( intersection of A and B)

Unfortunately most people are counting by adding A+B which results in double counting as person X who died in set B is also in set A.