Is there anyway someone can tell if you looked at their Twitter?

Generally people cannot tell who has been looking at their Twitter site. However, depending on how you reached their site they may be able to. Did you go directly to Twitter and find the specific user, or did you click an external link to reach their page? If you clicked a link to get there, they may have used a link cloaking service such as bit.ly or another that has an analytics function. If they did, some information may appear such as the page you came from what else you clicked and so forth. There are services that will even identify the IP address the user came from. Itshrunk.com does provide IP addresses. If the person in question does and Ip Address look-up, they may be able to track you as a visitor.