Ah, I can see now where your confusion originates.
Yes, many Tomica cars were indeed sold under the Hypercity brand in the USA, whereas this thread is about the somewhat different Tomica Hypercity range as marketed in the UK - as clearly defined in the title: Tomica Hypercity (UK) Illustrated Product List
I need to be corrected if I’m wrong, but as far as I know no Tomica cars were sold as Tomica Hypercity in the UK or Western Europe, either singly or in sets, except for the Honda 4-pack and the Hino Profia petrol tanker listed in the lead post in this thread. I’m not counting the Hyper Blue Police and so on fictional vehicles.
The great thing about the USA Hypercity cars, for me, is the large selection of Plakids that came with them (re-branded as Tomi-heroes).