I don't think Kenneth was skipping number divisible by 3 or 5 (or both). I'm guessing that it is his solution that is confusing you, and probably the if not... statement.

Here's his code:

current = 1

while current < 101:
    if not current % 3 or current % 5 == 0:
        print(current)
    current += 1

Kenneth does explain this, so it might be worth watching again. He's just demonstrating two different ways to accomplish the same thing (one way on the divisible by 3 and one way on the divisible by 5) An if statement evaluates an expression to true or false. When there is an or then either part can evaluate to true to evaluate the entire if statement to true.

Part 1 is - not current % 3 - when current is divisible by 3, current % 3 is equal to zero which is false and by putting the not in front of it evaluates to true. Remember the not only applies to one side of the or. Any number divisible will result in a Truthy result and a the If evaluates to true.

Part 2 is - 'current % 5 == 0` - which is basically the same as above, just another way to do it and I'm guessing that Kenneth is just showing both for the sake of demonstration and wouldn't mix the two methods in real life.

Does that answer your question?