To be fair, that's 1 in 50 from a group that was relatively accomplished in an academic setting before the test. But I agree that it doesn't qualify as "genius."
The Mensa cut-off is top 2% of the general public. 98th percentile on an IQ test.
For the LSAT, they accept 163 as meeting that cut-off. Relative to other LSAT takers however, a 163 is 92nd percentile. So the top 8% of LSAT takers are qualified to enter mensa, or roughly 1 in 12.