Can it be possible to have any other condition that appears to be meth mouth but is not?

Yes: Enamel or dentin forming disorders such as amelogenesis or dentinogenesis imperfecta, or fluorosis can make teeth very prone to breakdown... In the presence of a highly sugary diet and poor home care without regular dental visits, a mouth could deteriorate enough to appear to look like meth mouth...

Dental neglect : Poor oral hygiene, diet high in sugars, dry mouthall will cause rampant decay.

Yes: High sugar intake ("mountain dew mouth" / sucking on candies all day, etc.), and eating disorders which result in frequent and long-term vomiting.