You are running into Command Function Equivalence https://www.mathworks.com/help/matlab/matlab_prog/command-vs-function-syntax.html
aAreaVec>0.5
is parsed as a relational operator comparing aAreaVec and 0.5
aAreaVec >0.5
is parsed as a call to a function named aAreaVec with parameter '>0.5'
which fails because aAreaVec is known as a variable and so cannot also be a function call.
The correction is to either use
aAreaVec>0.5
or
aAreaVec > 0.5
or to not have the code as the first expression; for example it would work to use
disp(aAreaVec >0.5)
