Just brushing up a little bit on the definitions (I've also put integral calculus a long way behind me)
From wikipedia (
https://en.wikipedia.org/wiki/Improper_integral):"an improper integral is the limit of a definite integral as an endpoint of the interval(s) of integration approaches either a specified real number, positive or negative infinity, or in some instances as both endpoints approach limits"
And sos math (
http://www.sosmath.com/calculus/improper/convdiv/convdiv.htm... explains how improper integrals can be convergent (the limit exists and is a number) or divergent (limit does not exist or is infinite).
I presume here we're using the word calculate to refer to getting a numerical value, but in the case of an improper integral, this isn't always possible. So the course would be talking about calculating only convergent improper integrals (but convergent isn't specified in the source text).
There are tests to apply to establish whether the improper integral converges or not, and these would fall under calculus, not a calculation. This is what I think they're talking about in the course (i.e. rules, theory and proofs of why it is the way it is)...and that is calculus.