Because his jeans are so dressy, his simple top relaxes the look. The shirt has a relaxed fit, making it comfortable for long days at the office, but it is wrinkle-free and made with a nice fabric. (A t-shirt that is pilled, stained or well-worn wouldn't work in any office environment.)
His shoes - which lean towards the "dressy" end of the spectrum - complete the look, making it polished and professional without overdoing it.
