Someone misinformed you. There are two models:
Quote: Sigma makes two flash units which appear almost identical but differ significantly in features.
EF-610 DG ST — relatively inexpensive, but very powerful and capable.
EF-610 DG Super — keeps the same high power and adds wireless P-TTL, high-speed sync, better manual control, and a few more features.
Only the Super not the ST is wireless P-TTL capable.
---------- Post added 07-09-15 at 01:54 AM ----------
Source:
The Definitive Guide - Pentax P-TTL Flash Comparison
The site is aging a bit but still fairly accurate.