In this case, it sure does sound like abuse. Considering the careful wording, combined with the seemingly kneejerk reaction of requiring authentication, there was likely illegal activity going on:

Earlier this year we saw an increase in the number of reports we received about some people using our service in ways that we cannot tolerate. To be more clear, this was not about some people merely saying things that others disliked.

Over the past several months we tried multiple strategies in order to end the violations of our terms of service. However in the end, we determined that requiring authentication was a necessary step to continue operating meet.jit.si.

It was a free, anonymous service that let people stream video and send messages. Consider for a moment if that "video" was actually non-video data encoded to be streamed through Jitsi and sent to another location. Or, consider if the video was video, but was so egregious and illegal, that Jitsi had to take action. It doesn't take a lot of thinking to consider the kinds of activities could have been going on.