Tristan was equally afraid of Ashley and the old Alpha's return. Back then, the warriors had confirmed that the old Alpha was dead, but before they could return the body to the pack for a befitting burial, it was nowhere to be found.
The warriors had initially lied, claiming that they forgot and had not paid attention to Scarlet's instructions, and cremated the body.
Tristan saw through them, demanding to see the ashes at the exact location where the cremation was done before they confessed.
However, no one thought that the old Alpha would survive those injuries. He had been confirmed dead. Should he return, Tristan had no doubt that he, Scarlet, and all the warriors involved would be put to death.
Lunas and some betas were honored with a burial instead of cremation under the belief that they might return as a different person.