From the same page:
"Customers who have the Service NSW app installed will be taken to the check in.
Customers who don't have the Service NSW app installed will get two options:
- download the Service NSW app, create an account and check in
- check in using an online form."
Basically, you're under no obligation whatsoever to use the Service NSW app. If you don't have it, or simply don't want to use it for checking in at venues, the online web form remains an option - at least for now.