Are some Optus kiosks in Sydney Airport a scam?

In the international terminal of Sydney Airport there are several Optus kiosks. When I flew to Sydney for the first time, I didn't know that, and I proceeded to the first Optus kiosk I saw (assuming there is only one Optus kiosk in this terminal). I knew that there was a promotion ongoing that would get you 35GB of data for 15AUD (it was in July-August of 2019). However, when I asked the people at the kiosk about the cheapest plan, they said that 30GB for 40AUD was the cheapest plan. Assuming that the promotion I had in mind ended, I went ahead and purchased this plan. But then as I saw another Optus kiosk, and there was an ad "35GB for 15AUD; promotion valid until August 26" (I flew to Sydney well before August 26).

So I was wondering if the kiosk I used was some kind of a scam?

Here are some additional things I've noticed:

• That kiosk, as far as I understand, mainly targets Chinese and Indian tourists. (They were trying to get attention of Chinese and Indian people passing by by speaking to them in Mandarin and Hindi.)

• I was offered a 5AUD "student discount". I agreed. They said there was a 2AUD fee if I pay by card, I said ok. But the final amount I was charged, as per the receipt was more than 38AUD. 2AUD is more than 5.7% of 35AUD, which in hindsight I think is a ridiculously high fee. Plus I have no idea why I got charged more than 38AUD instead of 37AUD.

• I haven't found the kiosk I used on Google Maps. The kiosk that had an ad about 35GB for 15AUD is on Google Maps though. Also, the kiosk I used didn't look stationary (as opposed to the one which is on Google Maps).