Autism / Autism Spectrum Support Group
Autism is classified as a neurodevelopmental disorder which manifests itself in markedly abnormal social interaction, communication ability, patterns of interests, and patterns of behavior. Although the specific etiology of autism is unknown, many researchers suspect that autism results from genetically mediated vulnerabilities to environmental triggers.

People all develop differently, but losing skills, regression, is concerning.
How are you responding to the accidents? Have they increased since you've been responding that way, or have they decreased?
What does your son say about the accidents? Does he say he forgot, or didn't realize he needed to go? Or, something else?
The person who is telling you to let the stress dissipate is right. Reducing the stress may not solve the problem, but it will help.
I hope any of this helps, but for sure know that this is probably just a temporary setback and once you get through it he'll be back to whatever was normal for him.
Best wishes and blessings