One is likely to cause a few quid of damage. One is likely to seriously injure or kill. Completely asymmetric reactions and consequences. Particularly as the door kicking was a reaction to their safety being threatened.
If throw a milkshake over someone who was putting me in danger I’d expect and probably deserve a reaction. If that reaction was for them to shoot me that person should be put in prison for life.
What does kicking the door do that would make the cyclist safer?
If things escalate the response will obviously be asymmetric. Those of us trained in such matters call that an "impact factor", something to be taken into consideration when determining the safest response. That's why those who are genuinely concerned for their safety don't go there.
After all, if safety was genuinely his concern them why willingly commit an act to escalate the situation into an even more dangerous one?
You can't be genuinely worried about safety on the one hand, yet actively promoting and then participating in a dangerous confrontation on the other.
If you pick on a bully you cant complain when they turn round and smack you back even harder. You cant take back a good hiding, and being aggrieved over something doesn't make it hurt any less when they respond.