I'm pretty sure the short answer is: "Well, 4chan, right?". But it goes a bit beyond that.
If there's something that I have learned is that your standard :le-pol-face: is nearly IDENTICAL to ISIS, it's just a matter of whether they want to be a Christian CHUD or a Muslim CHUD. Osama Bin Laden was found to be a fan of anime too, among many other ISIS/al Quaeda members. Hell, ISIS members are frogposters just as much as "defend the west" CHUDs. There's a joke online about how fashy a lot of weebs are and I really don't understand it.
Anime is Japanese and Japan fought on the side of the axis is the only connection I can think of, but it's not like Japanese people are considered white in the US, the country that these hogs apparently love so much. Hell, hogs demonized the FUCK out of Japan in the 70s and 80s too despite being a fellow capitalist nation. Now they're coming around?
Also, look at two of the most popular anime: Pokemon is pretty pro-environment and Dragon Ball Z: where Frieza talks almost identically to your average chanbrain and was inspired by real estate speculators because of how evil they are.
Is there a deeper connection besides "4chan lol"?
i think you're muddling ISIS and chan terrorists a bit too far. ISIS is a religious fundamentalist organisation, but was also founded in the milieu of resistance against american occupation. its membership outside the odd euro larper was experienced guerillas & former army. materially and organisationally they're leagues ahead of chan terrorists, who still aren't mostly affiliated with real groups
that's because ISIS mainly exists because Saddam Hussein's army was laid off with no pensions and found themselves unemployed