When they said very quickly upon review that "both arms" were "involved" in the "tackle" I could see that one of those arms (his left) was on the ground supporting his body weight!
I suspect this is true given how often we got caught behind the ad line going nowhere over multiple phases. The law for rucks is behind the last feet, so was this just not being policed or are the Lions defenders just very quick off the line? Would be interesting to see some footage from above.