Well, that was speculated as a possibility. Most of the university’s presidents have had some affiliation (past or current). In a few cases, complete outsiders have been chosen. See this comment for the tally, and note that Alivisatos makes nine with prior affiliation: New President Search -- any updates or rumors? - #14 by JBStillFlying
The natural position for internal promotion would be provost, but Lee has only been on the job for a year. Had she been chosen, that meteoric rise would have probably been second only to that of the wunderkind himself, Robert Maynard Hutchins. The prior provost is now running Vandy. The last provost before him is now running Cal Tech! So perhaps they just felt it was time to reach out to those who have an affiliation with the university - and hopefully a clear understanding of its particular intellectual culture.