Lo and behold, the patent [1] says:
> [0038] In preparing the xenograft for use, the tendon is surgically dissected and removed from the paratenon (tendon sheath). The tendon is composed mostly of an extra-cellular collagen matrix, which is non-immunogenic. The tendon may therefore require no denaturing (decellularisation) prior to implantation into a mammal. In some embodiments, the tendon may be subjected to a decellularisation process prior to implantation. In removing the cells from the tendon, the immunogenic antibodies within the cells are also removed, thus rendering the tendon non- immunogenic. Methods of decellularisation of tendon tissue are known in the art. Such methods include physical, chemical and enzymatic treatments, wherein the cells within the tendon are lysed, leaving an undamaged extracellular matrix having the same physical and biochemical properties as the natural tissue.
So it is decellularisation, they aren't claiming any particular decellularisation method, but it's quite possible they have some particular recipe for decellularisation which works well, and which they are keeping secret.
[1] https://patents.google.com/patent/WO2019014698A1/en?oq=20179...