This is correct. Whether the proscription of Palestine Action was right or wrong, there are many ways people can legitimately and legally protest about Gaza. And regardless of my views, I support their right to do that. Supporting a banned organisation isn't one of those ways however.
Yesterday was akin to someone driving their car and ramming a mobile speed camera van, resulting in a driving ban. Then driving past another, while serving that ban and flicking a v-sign at it.
And imagine if it was Yaxley-Lennon leading a march supporting a proscribed far right group. I strongly suspect the same people complaining about people being arrested en masse for supporting a banned group wouldn't be quite so vocal in their protests about mass arrests in this case.