I honestly thought that nobody in their right mind would put that combination of fish in a 75.
Ah. I used to help out at my friend's fish store, and it doesn't surprise me at all. People are crazy, ignorant, outright don't listen, or all three.
I once saw a woman's kid ask for a betta for the little critter creeper they were buying and she screamed at him "That tank is too big for those!" and pulled him away. She then proceeded to buy 6 baby comets....
And I'm not a tank measuring expert, I've just bought and sold a lot of tanks, and viewed lots of pictures on craigslist. I didn't mean to come off rude, you just get an idea of what certain tank sizes look like in pics when you view pictures all day looking for tanks to buy.

And 75g and 55g seem to be the most common "huge tank" (as described by online sellers) for sale, so I've seen a lot of them. Also seeing arows and big cichlids in 75g or even 55g tanks isn't uncommon if you browse online ads.
As far as fish sizes on ads, take that with a grain of salt. Just about everyone over exaggerates the size if they're looking to sell fish to people looking for big ones, and understates the size if they're looking to pawn off a big undesirable fish on someone.