So 3 VHFs engaging a battleship would be considered ganking?
3 transports vs 1 bomber is considered ganking?
3 bombers vs 1 BS is considered ganking?
I'll put my answer plainly; No. Your ideas of ganking are very far off the mark. For one, you're claiming 3 bombers on one cruiser is ganking.. Then pray tell, what number of bomber is appropriate for a cruiser? You're a bloody capship, learn to get some escorts smaller than yourself. You're not meant to kill a bomber group on your own. Bombers exist for the sole reason to kill capships. Get used to it.
While what happened in the video may have been a gank, there are many other situations where such a thing is not a gank. It would also be very hard to enforce. And lastly, ganking, while it can sometimes be unfair, is also a very in-RP action. The Liberty Navy wouldn't hold back its forces against an RM invasion fleet, they'd send what was needed to destroy it with as few losses as possible. ie; Gank it. Whether the player faction decides to do this or not is up to them, and should never be something demanded by the rules, as that could cause unfair situations like the three at the top of my post.