That figure of 337k+ is as of the November reporting date and it was 196k a month earlier, 139k for September. Short interest grew by 41% between the September and October reporting dates. The price of the stock was on either side of 24 around the September date. The price was around 23 near the October reporting date. The price of the stock was near 34 at the time of the November report, with the short interest increasing month to month by 73%.
As the price of the stock increased the short interest grew as well, in fact at a greater clip than the appreciation in the stock. PMTI and ELOS have a much higher percentage of their shares outstanding being short. One would expect that with the continued increase in share price since November (now at 42+-) that short interest has increased by a relatively large amount again this month.