They did not gain $2.9 billion in cash from that. The transactions gave Uber ownership stakes in combined businesses. They got 27.5% of Grab. They got 36.6% of the Yandex merged entity. The gain referred to in the article is for accounting purposes.

https://arstechnica.com/cars/2018/03/uber-sells-southeast-as...

https://www.bloomberg.com/news/articles/2017-11-24/uber-s-pl...