runner assisting another runner

[Little Jimmy]

A fellow blue relayed this to me tonight and wondered if he made the right call. NSA fastpitch.

Runner on first. Batter hits a ball deep to the corner for a hit. As runners advance the batter runner keeps catching up with R1 to the point where she is directly behind her when they are a few feet from the plate. As the ball approached the infield, the trail runner "playfully" ( says my ump friend ) pushed R1 to the plate and then crossed it herself. He called R2 out for interference for assisting R1.

I don't think he got it right. Even though it seems like something wrong happened I find nothing in the rules disallowing the action. In fact NSA 8-8-n speaks of anyone other than the another baserunner being out if they assist ( ASA 8-7-E states the same thing. R2 never passed R1.when she pushed her.

The bottom line is this; is physical assistance between runners allowed so long as trail runner doesn't pass lead runner? I can't find anything ( NSA or ASA ) that specifically says its OK but it seems like it is.