The definition of 'shill' hasn't changed.
A shill for the DNC is a political job on the internet. It is a legitimate job. You get paid for it (as much as when you are canvassing, anyway). A shill works in an online forum mostly, but sometimes works as an administrator.
Nine people just don't walk up at once to bash on ICE. They come in one or two at a time. An intelligent discussion is only attractive to a leftist if it has lots of leftists working on derailing it. It's no fun mindlessly regurgitating alone or with just one other troll...the cowardice overwhelms very quickly.
A shill hurls ad hominem. He uses his own credibility and political equity. He, like other shills in the game are there to start the shit-slinging, making it attractive for other leftists to join the thread. As seats fill in, shills throw their grenades and step aside, always leaving a couple of talking points unmentioned. Shills are under no obligation to be honest in any way, and they will never identify who they are if asked. Most shills are also affiliated with someone's campaign.
Since you are throwing away your own credibility, shills often are 'cowards', fleeing to the hills early, and doubling down only when advancing a dishonest narrative when all the details haven't had time to come out. Such players are losing credibility, little by little, until they have none at all, due to the indefensible nature of the DNC and its Marxist policies.
So, a shill is a legitimate job. They are a fake "neutral, unbiased" poster to get a troll sub-thread started. The more troll sub-threads started, the more bandwidth the forum will need for them. It's a win for the shills, it's a win for the party, and it's a win for the leftist cowards. Posters now have a choice of sub-threads in which to bash Trump. The forum is getting more views from the lurkers. More vigilance is needed to enforce 12B and other forum rules, and to monitor all those active posters.
Why he considers a 'shill' to be some kind of insult is simply because he doesn't know much English.