Something is off in your numbers. Swarthmore has much, much more than 1.8% Jewish students. Swarthmore is quite small – only about 1,600 students total. If its Jewish population were 1.8%, that would amount to fewer than 30 Jews. Trust me, there are many more than 30 Jewish students at Swarthmore (and lots more Jewish faculty, too).
For that matter, 17.4% seems awfully small for Penn, but I can’t say it’s completely wrong. The presence of lots of Jewish graduate and professional students (and faculty) means that there is a large, vibrant Jewish community there – actually multiple large, vibrant Jewish communities. In the past 50 years, Penn has only had one non-Jewish president!