Yeah everyone should be equal, all stats are 10 from everyone.
But being a fixed stat modifier it technically is innate (even if they pretend it isn't from birth, it is from the circumstances of their birth in some instances Noble for example), they are saying poor people are stupid.
It's not a racist idea. A child (halfling) is clearly weaker than a 6' 8" man (Goliath), there is nothing racist about that, it's just an obvious biological advantage. Similarly there is no reason average intelligence can't be different between species, clearly some animals are smarter than others.
What is concerning is saying a child born to a poor background will be thicker than one born to high society. If they had a stat called Education rather than Intelligence, they might get away with it.