This is correct. Substack was one of the first "mainstreamish" platforms to go "against the grain" and try to be neutral with respect to the topics and ideas it platformed. Notably, it allowed deviations from the "party line" on the issues of the pandemic. As became evident with the SPLC story, there are powerful organizations whose goal is not to forget such things and organize persistent media punishment campaigns against the dissenters. This can well be a manifestation of that.