They may have got the idea from the first J-Pop Cute / Metal crossover... 
My understanding is that many Band-Maid fans take offense at comparisons to BabyMetal, because a Band-Maid is a home-grown band of musicians who play their own instruments, while BabyMetal is essentially manufactured by an executive of a J-Pop powerhouse, and the girls essentially are just singer/dancers fronting a band made up of session musicians.
I think the contrast is a bit overblown. The executive in question was apparently a big fan of metal, and felt that Suzuka Nakamoto had a voice and vocal range better suited to metal than J-Pop, so creating BabyMetal was more a fulfillment of a dream than a marketing gimmick. And on the other side, Miku Kobato, the founder of Band-Maid, herself didn't play an instrument when she created the band. She was originally to be the singer, but decided her voice wasn't well-suited to the music, so she recruited Saiki Atsumi. Miku has essentially been learning to play rhythm guitar since the band's debut, and has to her credit improved considerably. For what it's worth, in my opinion, Suzuka is a much better singer than Saiki.
BabyMetal has this weird mythos about the Fox God creating the group to bring metal to the masses. So, you have a group fronted by singer/dancers better known for other things than rock, backed by some of the best session musicians in the business, and on a mission from God. Sound familiar?
Again in my opinion, while "Gimme Chocolate" was BabyMetal's breakthrough, especially to Western audiences, it's a bit too pop to be a good representation of the group's range. Road of Resistance is good:
This performance at Sonisphere UK in 2014, where they had been unexpectedly moved to the main stage with little notice, famously won over the Western metalhead crowds.
