Although instructors in higher education are oftentimes content matter experts, they may not have received training on instructional design or inclusive practices, such as Universal Design for Learning. However, instructors may serendipitously implement aspects of UDL without full knowledge of the framework. This qualitative study used sensemaking theory to explore interview data from 33 online instructors with ten or more years of experience in online education to explore (1) what aspects of UDL online instructors serendipitously used when designing and teaching online courses and (2) what aspects of sensemaking online instructors used when describing their serendipitous use of UDL. Analysis used an adapted phronetic iterative approach and revealed several themes. First, analysis indicated that instructors used aspects of all three principles of UDL when designing and teaching their courses: Engagement, Representation, and Action & Expression. Second, analysis found aspects of sensemaking -- Noticing, Bracketing, Labeling, and Acting -- with 11 full exemplars, demonstrating instructors cognitively working through the full sensemaking framework in speaking about their serendipitous use of UDL. We suggest that sensemaking explains how instructors might incorporate parts of UDL into their course design without knowing about the framework. Further, we suggest that sensemaking could ease instructor transitions from serendipitously implementing strategies aligned with UDL to deliberately designing a course using a robust understanding of UDL as a framework. [Note: The page range (177-195) shown on the PDF is incorrect. The correct page range is 177-198.]