It is. Trunks in base form have around 84,000,000(84 million) power levels. With Ssj it got a 50x multiplier and resulted in 4,200,000,000(4.2 million). Trunks do not have 1 billion power level. Therefore it is not multiplied by 50x to result in 50 billion power level. 1 billion is only used to state that Trunks in his base form is not even 1/8 the power base of Goku. Sorry for the long explanation.

Beerus, Super timeline, Dragonball multiverse and alternate timelines as a whole will be introduced after Omega Shenron's defeat.