I'm confused by this... It seems to me like the relevant part is "playing computer games is good" not "the type of sitting you do matters". Playing computer games while standing might be even better
It's probably more "active" sitting. If you are a gamer (especially computer gamer), you are generally not just sitting back "relaxing". Your body is more engaged and you are constantly moving your body in some way.
Sitting and watching tv you can literally be completely still for long periods of time.
"A professor at the Institute for Work and Health found that people who stand throughout the day at their jobs have a 2.2 times higher risk of developing heart disease than those people who sit during the day." https://www.ergolink.com.au/blog/standing-vs-sitting-at-a-de...