They probably just meant Xebec, or the pirates going on an all out brawl
Kaido at his prime in hybrid form could barely make a crack through Onigashima‘s roof
Destroy the island my ass
Blast breath and flame dragon are his only good dc moves
This is because Kaido had already complained about Linlin blowing up Onigashima (also Luffy is rubber, he bounces off the ground naturally, lol).
Kaido's ability to produce such destructive attacks without destroying much of his own fortress actually shows his Haki/skills are very refined.
Flaming Torch Dragon melted Onigashima's horn off; Kaido can easily destroy Onigashima. The only parts of it we saw him destroy were parts he could rebuild easily/weren't necessary to begin with (hence Oda using the horn to show Flaming Torch Dragon's power: the horns on Onigashima are purely decorative, Kaido doesn't need them).
I think Kaido can destroy Onigashima outside of Flaming Torch Dragon, but, yeah.
Kaido, Linlin, Akainu can all easily blow up small islands with their Fruits/Haki. Look what Doffy did with the Birdcage, come on, now.
Kizaru and Kuzan can, too, but Kuzan would probably need to freeze the island, then punch it hard enough.
I don't think we've really see the Admirals strongest stuff yet. Same with Linlin and Kaido.