Looking at the highlights on Alty TV. It is a sending off. It is a bad challenge. But if you mess about in the corner wasting time you invite that challenge. I can't understand why the assistant didn't flag when it is right in front of him. Unless the refs were
mic'd up with each other.
That looks like a dreadful 'challenge' by Holness and fully deserving of a red card.
Here's a possible answer to your point regarding the assistant referee, as suggested by a friend and fellow Alty supporter:
"The linesman hears the whistle and assumes the ref has blown for the free kick and not full-time so doesn't flag.
The liner is obviously aware of the challenge and informs the ref when they come together."