Can you tell me how are psychologists able to distinguish the differences between being a schizoid and asperger's syndrome?

Schizoid Vs Asperger: Asperger typically shows more severe interpersonal interaction and stereotypical behavior than Schizoid Personality Disorder.

Difference: Schizoids are indifferent to interpersonal relationships. They simply don't need people. Those with Aspbergers do need relationships with others but are hampered by an inability to read social cues, black and white thinking styles, abrupt communication styles, and social awkwardness.