They almost certainly mean triple compared to lithium ion (similarly for the 90% less energy claim). Lithium ion batteries currenty hit a maxium energy density of around 265Wh/kg, with a theoretical maximum of around 400-500Wh/kg[0][1]. Lithium sulphur batteries have a theoretical maximum of around 2500Wh/kg.

[0] https://cleantechnica.com/2020/02/11/lithium-sulfur-batterie...

[1] https://www.lis.energy/site/li-s-energy-applications/lithium...