There are two probable answers to this:
They are talking about Telstra Customers who generally have a contract with Telstra that has the terms regarding when NBN is available they will swap you from ADSL to NBN. They will just carry out the swap and your ADSL is defunct.
or
Regardless of who has or has not swapped after the 18 months the ADSL connection is cut and you are without internet until you either connect with the NBN or you use an alternative means eg wireless data. This connection to the NBN can take months. Most people are encouraged to swap before this end date to avoid some of the time issues (doesn’t always mean a smooth transition).
This has occurred because the ACCC took RSPs to task, and made them refund customers, over their claims of speeds available which many were unable to achieve. So now you will be told the more truthful answer about possible speeds. I think they will be trying to sell you the 50/20 Mbps package from the speeds they are quoting but the upload looks terrible from that perspective and you might be better off paying for the 25/5 package instead. Not a good answer but it is the honest one 
No it isn’t illegal to record conversations, just there are rules to follow depending on location and the means of the conversation eg face to face or over a telephone and the State or Territory you are in.
From https://www.corneyandlind.com.au/resource-centre/schools/privacy-and-the-recording-of-conversations/
"In many cases it not unlawful for private conversations to be secretly recorded without the knowledge of all participants. There is no obligation to obtain the prior consent of the other parties to the conversation. The secret recording may potentially be used in subsequent legal proceedings.
As a general rule, in Queensland*:
it is illegal to record a telephone call with a device physically attached to the telephone – Telecommunications (Interception) Act 1979 (Cth);
it is legal for a telephone call to be secretly recorded by an external device (e.g. Dictaphone) by a person who is a party to the conversation – s 43, Invasion of Privacy Act 1971 (Qld);
it is legal for a face to face conversation to be secretly recorded by a person who is a party to the conversation – s 43, Invasion of Privacy Act 1971 (Qld);
it is illegal for a person who is not a party to the conversation to record a conversation (whether by telephone or face to face)."
This occurs due to a number of factors:
The fact we have the Malcolm Turnbull NBN design and not the Rudd design, so many places that would have had FTTP now have a variety of connections.
The situation that city folks pay more than they should for their connection so that other folks pay less for their’s than they otherwise would. It is called uniform cost:
Very slowly unfortunately and that isn’t a really satisfactory outcome. Want faster? Ask your Council, or your suburb or your block or your street to submit a “Technology Choice Program” application if they are willing:
It is costly but some of the costs can be shared.
As a final note if you are unable to achieve 25/5 Mbps then you may be able to attempt to request to get a different type of connection as it doesn’t meet the mandated requirements, but this can be doubled edged in that you may be put on a satellite connection which @gordon has, can and will attest to, is terrible. But if it is a larger area of people you may be able to fight for a much better connection than whatever they are currently offering/supplying.
