At the time of that article, antifa had been linked to 0 deaths in the last 25 years. So what if someone tweeted support? Antifa is not the lefts version of the KKk.
That's assuming there hasn't been a some kind of institutional coverup, abuse of gaps in statistics gathering due to insider knowledge, or denialism.
Someone like Michael Forest Reinoehl openly declares his support for Antifa and shoots someone for politically motivated reasons, yet still somehow that terrorist organisation has counted for 0 deaths in 25 years, you kind of have to start asking what's going wrong with data gathering.
... Oh look! Your source is from 27th of July, just before the famous shooting! Convenient, that, eh? It's almost like starting terrorism deaths in america stats in October 2001.
Statistically, someone in an "organisation" that widespread, operating for as long as it has (much longer than 25 years), and in rougher times in history around the world must have at least knifed one right wing politician in a backalley in Germany.
It seems possible to infinitely atomise, devalue, deflect and ignore attacks by left wing terrorist cells in first world countries in ways that people never seem to do with the universally accepted blankets applied to far right or islamic terrorism.
My guess is that a lot of the coverups can be attributed to its cell based/word of mouth structure. Even when an attack is somehow clearly attributable to politics (and opsec makes sure that operatives tend not to claim responsibility, and make it look as much like a random incident as possible), when the People's Front Of Antifa Cell can be proven to have killed someone, it's not attributed to other umbrella groups with the same name and goals like the Antifan People's Front.
Deaths in riots caused by BLM protests never get attributed to BLM, but four people dying in and around the senate storming of various causes all get attributed to the far right as a whole.
It kind of flies in the face of how we calculate deaths attributed to other distributed, cell based groups like the Taliban, but the standards seem to be different whenever you talk specifically about left wing based terrorism.