The aim of this stream was to make a nice collection of happy birthday wishes for her art mama KT. KT has been very supportive of her (and other niji members). Enna even did a karaoke for KT a few years ago, but wasn't able to this and the past year. She picked this time slot and did the stream unannounced hoping KT wouldn't notice to make it a surprise (KT lurks her streams quite often and sometimes comments in the live chat). The stream was planned to be unarchived from the beginning for the same reason.
Due to how the drawing website works someone on twitter was able to clean up the 4 canvases and posted them on twitter (essentially everyone has their own layer and you can turn off the layers from other people).
I don't really get what they were trying to accomplish here. Enna was not even doing this for herself, she wanted to show appreciation to someone who has supported her since her debut. There are many good arguments against Niji, but this just makes them look like generic antis.
Enna herself wasn't to bothered by it, she hid the canvas pretty early and told everyone to just export their own drawings and post them on the hashtag on twitter, which many did later.