>>> The second reason software is slow is known as space complexity. This is a measure of how much 'space' or memory a computer needs to run your solution. The more memory required, the slower the solution.
Requiring more memory doesn't make an application slower by default. It simply means it requires more memory to run as expected.
Similarly, when he's talking about run time complexity, he calls it "a measure of how many comparisons a program needs to make to achieve a result". It can be any action, not necessarily a comparison. Be it number of times cycle needs to be executed, number of expensive calls to external service, etc. Number of comparisons to make is commonly used in introductory courses when studying sorting algorithm but doesn't make much sense without a context.