The Corporations Act defines a substantial holding as a holding...

The Corporations Act defines a substantial holding as a holding of 5% or more under the control of a shareholder or associates.

If a shareholder acquires a greater than 5% interest, they have to lodge an announcement with company and ASX. Forms must be lodged within 2 business days of going through 5% limit or by the next day in a takeover situation

Once gone through 5%, announcement must be lodged for every 1% change.

So, if M&G shareholding had been sold to one party (or group of associated parties), they would have gone through the 5% limit (subject to the 2 business day disclosure) and would have had to lodge a notice of initial substantial shareholder with the ASX

As this has not happened (yet) - answer is no one knows, so probability is that the shares sold have gone to a number of unrelated parties who each hold less than 5% of CDU

As a previous poster stated - perhaps the CDU employee share plan (as the beneficial holders are not associated, so should not represent a single substantial shareholder - but I could be wrong) plus perhaps a whole heap of small investors