Or it's the simple matter of doing a deal with a large entity /...

Or it's the simple matter of doing a deal with a large entity / company requires many ticks of approval to go ahead. Hence a lot of people know about it before the market does.

People talk regardless of confidentiality. Whispers are heard that company "ABC" is signing a large deal with IAM. They look at the IAM share price and see it is an attractive buy at these prices for the type of deal they have heard whispers about being executed. They buy on this knowledge.

They can't do this with their privileged knowledge if IAM is in a trading halt can they?

We can talk about this either way good or bad. There's always two sides.

Fact is it's all speculation and none of us know.