It’s a mistranslation of the Hungarian ügynök, which can indeed mean agent, but not necessarily. Here it means informant/source.

I appreciate the title is wrong, but no reason not to add the correct context.

Yes, and the first sentence used the word “informants”. See my comment above.

"And agent is not the same as informer"

The difference is not really clear in reality and can get blurry quickly. Informants can also be ordered to do more active things to get information - or spread missinformation, or be ordered to do other active things. Simple things like luring a person to a party, or using their influence of position to prevent or make something happen (punish/promote a student/worker, make a certain result go away, ..).

So the majority were likely passive informants with the job of writing reports, but not all of them. And to me it rather would matter if they took the job voluntarily or were forced to do it.

Agents vs informants is a venn diagram. Some informants become active participants under orders of an intelligence officer, they are instructed to use their access for further tasks. Some agents infiltrate groups and inform their handler on group activities and membership. Not all agents inform (they may perform things like sabotage or murder) and not all informants are instructed to do anything (they are paid and never contacted again).

There are several Chinese informants caught in the last few years in Western countries, a lot was just doing it for ideological reasons, the monetary reward really doesn’t match the troubles involved and the severity of the crime

That information may come in spring when the B files drop.

Many became informants because they were approached by agents asking them to tell them everything they knew about a target. Pretending to not know anything was risky. If they discovered that you didn't tell them about something you should have known, it was your ass that got sent to a re-education camp. If they as much as suspected that you were withholding information, you may have found your job suddenly relocated to some forgotten corner of the country.

If you think, i'm exaggerating. My grandfather, a prominent writer, was exiled to teach elementary school in far-off village for a few years after one of the ruling elites decided that his latest play was unsympathetic to Communist ideals.

Your silence about ice cream is very telling...