"But somehow this drawing style"
(puts on Tinfoil Hat 9000)
Theory 1: The way that phrase is told makes me think that the Onryo's artstyle probably reminds him of an artstyle of a certain artist but he just can't fully recall it for the moment, and the way Onryo-chan blushed... What if back when Onryo chan was still alive she's a fan of MC and became a mangaka with her artstyle close to MC's but then she died because she overworked on a deadline project or something then she became a vengeful spirit to MC because maybe she blamed him for her death but lost motivation or something to actually harm him...
Theory 2: I may have just be thinking of this too much because it's 4am and he probably just mean that Onryo-chan did a great job copying his artstyle and she's blushing because she notices he's looking at the pages intensely