Newt is noticing some strange similarities between Credence and Percival (wolfing down meals/reluctance to toss away broken things/discomfort with spending money on non-essentials). Credence has noticed them too actually.

They're curious. Percival, with his old family and everything that comes with, should have grown up like a prince surely.

Turns out the Graves family are much better at keeping up appearances than they have at managing their finances. By the time Percival was born they were skint.