You are both right. Methane has a Global Warming Potential of 86 tonnes CO2e over 20 years, 25 over 100 (because it breaks down into CO2).
The methane release of the tundra/taiga is one of the huge negative feedback loops that terrifies climate scientists, along with the possibility of the Amazon moving away from the massive CO2 to O conversion system that has been to a rather closer to neutral system like the northern boreal forests.