Marlon says "That's the 'Big Guy'. Quite a paintbrush he's got." Explain the dramatic irony of this line

Marlon says this to Truman when Truman reveals his wanderlust to his oldest friend. Christof uses the emotional ploy of emphasizing the beauty and perfection of Seahaven Island to prevent Truman from wanting to leave. However, Truman's innate curiosity ends up being more powerful than Christof's "paintbrush." This line is also a nod to the film's religious undertones. Marlon uses the phrase "big guy" which could colloquially mean "God" or some kind of omnipotent entity, but in this case, Marlon actually is referring to Christof. Christof is the big guy with an actual paintbrush - and while he has the power to create his own version of "perfect," Truman does not necessarily prescribe to his vision - partially because he has never had the opportunity to see anything else.