Well, I can't help thinking that Bos was just trying to keep upright. A sling as has been noted would have sent him to the right, not the left. He's from the track ffs. Plenty of experience riding close.
Impey was bouncing around the field in that sprint. Personally, Bos there or not, I felt he would have gone down at some point.
Not sure Bos covered himself in glory, but equally not a bannable offence IMO