" APM’s senior economist, who estimated more than half the sales are by investors, many of whom are seeking capital growth from property in their self-managed superannuation funds."
I think you've misinterpreted that statement which probably isn't worded as well as it could be.
I think they are saying that half the sales were made to investors for their SMSFs who are chasing capital growth from property. There is a pretty big push into property via SMSFs by the spruikers lately.