It's a bit of both, I think. There will always have been some minority with these views (every party attracts some eccentrics, including some racists) and now that the Greens are becoming more electorally successful that's brought the new scrutiny that's revealed this and other individual's views.

Unfortunately there's also a history on the left of people who claim (or actually believe) that they're merely criticising Israel's policies, but do so in a way that's plainly antisemitic. Some of those people have of course joined the Greens as the major left alternative to/replacement for Labour.

Honestly, I hadn't seen much of this from the Greens till recently, so it's disappointing to see it coming to the surface now. What's even more worrying than the ever-present minority of antisemites (which, as I say, you could undoubtedly find in every party) is senior figures not taking it seriously.

It's also possible that there are infiltrators. It's an open system compared to the other parties, and subject to manipulation by bad actors.

Now that their membership has grown so much, they'll have to add additional safeguards to prevent abuse of processes.