If 'violence' has been re-defined to the extent that mis-gendering someone is an 'act of violence' (https://everydayfeminism.com/2017/01/misgendering-trans-peop...), then you could certainly argue that ER have acted violently.
EDIT I see I'm being downvoted. Are we not allowed to have a conversation about re-defining words and being intellectually consistent with the re-defined meaning?
It seems these days that the word 'violence' has been re-defined such that it no longer requires there to be any abusive physical contact between the perpetrator and the victim. As such, merely using words that may cause an individual some emotional discomfort is considered an act of violence.
I don't agree with that definition, and for me abusive physical contact is the defining characteristic of violence. But if that's the general consensus now then that's what I'll use. We can't have a debate if we're all speaking a different language.
Given that 'violence' no longer requires any physical contact, one could make the argument that some of the activities that ER have engaged in could be considered violent. The many ER road-blocks have very real consequences for all the people who are unable to go about their daily lives without being disrupted. When ER blocks a bus full of people in traffic, it's distinctly possible that those people were on their way to job interviews, doctors appointments, meetings with long-lost relatives, charity fundrasiers or any number of other things. This kind of disruption might easily cause significant emotional distress, I would argue at least on par with the emotional distresss suffered by an individual being mis-gendered. So why should one be considered violence and the other not?
That's not even getting to the topic of Ambulances being caught up in ER road-blocks, which has been documented numerous times. ER even address that issue explicitly in their FAQ (https://rebellion.earth/the-truth/faqs/). They attempt to hand-wave this problem away by saying that ambulances can be re-directed away from the road-blocks. It hardly needs to be said that time is often a critical factor when an ambulance is transporting a patient to hospital. The additional time spent avoiding ER activists could easily be the difference between life and death. Is this not a form of violence?
By your own definition, the answer is clearly no.
One definition of violence appears to be used when describing ER as 'non-violent'. But another, very different definition of violence appears to be used when declaring that mis-gendering someone is an act of violence.
My answer to this is to insist on the 'proper' definition - the one you yourself prefer - and to push back whenever the term is misused (I find this is generally done as a smearing tactic).
The alternative is to yield ground and to start saying 'physical violence' whenever one means 'violence'.
It is the intentional or willful mis-gendering that is being argued in that link as being an act of violence.