Generally speaking:

• It’s possible to have credentials without being an expert.
• It’s possible to be an expert without having credentials.

Some specific examples

• Someone with Special Autism Training isn’t necessarily an expert in communicating with autistic people
• It’s actually likely that they’ve been thoroughly taught to be incapable of doing so
• People with rare medical conditions often know things most doctors they encounter don’t
• Someone with a college degree might not know as much as someone who studied the same subject privately

This doesn’t mean credentials are irrelevant – but they only tell you so much. Don’t confuse them with expertise.