Bigg Boss never used the word "bhag".

Bigg Boss never said that Rahul ran away while asking the housemates to choose two people for jail punishment between Rahul, Nikki and Aly.
They never used the word "bhagna". They just said "Rahul just chor kar chale gaye." or something like that.

It was only Salman who used the word "bhagna", but Rahul can't pick on Salman alone, so he included Bigg Boss as well to justify himself.

Salman obviously doesn't watch the show so he doesn't know if Bigg Boss used that word or not, otherwise he would've corrected Rahul, and blasted him much more brutally.