There was a short discussion on wisent apperance on one of the online bison meetings. Basically, hybridizing European an American bison is a constant problem. From an online photo, it can be impossible to tell the species, with different angle, individual variability, and especially if this is not an old bull.
I myself don't feel certain to tell wisent vs american bison vs hybrids from photos at the Silvertine website. Some indeed have full hair between horns and on forelegs, and keep the head low like American bison.
The EBPB writes: "After correspondence with the owner we updated the information about 6 European bison living at the Rockwood breeding centre in Canada. In April 2016, all were purchased by Mr. Steve Rahn, owner of the Silvertine Ranch. On that basis, information on the transfer of animals to a new breeding centre has been included in the table on Additions and VIII Corrections to former lists. Mr. Rahn has other European bison in his possession – which will first require testing for their genetic purity at the level of the species, prior to any inclusion in the book."
It would be interesting to know what is the history - and purebreed status - of the other probable wisents at Silvertine, and that another breeding ranch in North America mentioned on the website.