They might not be talking about the artstyle per se - there's a famous scene in Prince of Egypt (the 90's animated movie based on the story of Moses from the bible) where Moses finds a mural of Israelite babies being massacred after learning that he himself is an Israelite. I don't know enough about AoT to really understand what's going on here (nor do I particularly want to know), but "an upsetting revelation spurred on by a mural on the wall leading to the viewing character's inner turmoil" could qualify as "Prince of Egypt vibes".