Does GA flying in your own plane count toward a Airline Transport Pilot license?
The video isn't very clear, but most of the numbers it gives are "total time". This is cumulative, so the 1500 hours required for an ATPL includes the 250 hours required to get a CPL, which itself includes the 35-40 hours required to get a PPL plus the 15 hours required to add an instrument rating to your PPL. Also included in there somewhere will be 10 hours to add a multi-engine rating.

All loggable time counts toward the total. It doesn't matter if the aircraft is an airplane, helicopter, gyrocopter,  glider, balloon, powered parachute, etc. However, at least in the US, ultralights cannot be logged because they are legally not "aircraft".

As noted in the video, most aspiring airline pilots get flying jobs as soon as they get their CPL, most commonly as Certificated Flight Instructors. Many schools even guarantee a job as a CFI for students who graduate. Few people can afford tonrent their way to an ATPL, and it just doesn't make sense to use loans to fly when there is a shortage of pilots to take jobs where they can get paid to fly instead.