The reason that you can have two psychiatrists disagreeing on this matter is that whether one is considered hypomanic or not is somewhat subjective (in the eye of the beholder). An excellent summary on the signs of a hypomanic episode was found on pyschcentral.com:
Hypomanic episodes have the same symptoms as manic episodes with two important differences: (1) the mood usually isn't severe enough to cause problems with the person working or socializing with others (e.g., they don't have to take time off work during the episode), or to require hospitalization; and (2) there are never any psychotic features present in a hypomanic episode.
A hypomanic episode is characterized by a distinct period of persistently elevated, expansive, or irritable mood, lasting throughout at least 4 days and present for most of the day nearly every day. This hypomanic mood is clearly different from the person's usual mood.
During the period of mood disturbance, 3 or more of the following symptoms have persisted (4 if the mood is only irritable) and have been present to a significant degree:
- Inflated self-esteem or grandiosity
- Decreased need for sleep (e.g., feels rested after only 3 hours of sleep)
- More talkative than usual or pressure to keep talking
- Flight of ideas or subjective experience that thoughts are racing
- Distractibility (e.g., attention too easily drawn to unimportant or irrelevant external stimuli)
- Increase in goal-directed activity (either socially, at work or school, or sexually) or psychomotor agitation
- Excessive involvement in pleasurable activities that have a high potential for painful consequences (e.g., the person engages in unrestrained buying sprees, sexual indiscretions, or foolish business investments)
A hypomanic episode is associated with a change in functioning that is uncharacteristic of the person. For example, the individual may be far more productive or outgoing and socialable than they usually are. This change in functioning and in mood is not subtle -- the change is directly noticeable by others (usually friends or family members) during a hypomanic episode.
A hypomanic episode is also not severe enough to cause serious impairment in social or occupational functioning, or to necessitate hospitalization, and there are no psychotic features. The observable symptoms of a hypomanic episode must not be due to substance use or abuse (e.g., alcohol, drugs, medications) or caused by a general medical condition (e.g., hyperthyroidism or diabetes).
People who experience a hypomanic episode are often diagnosed with a type of bipolar disorder called Bipolar II.
I hope I was able to furnish enough information that you will be able to use in this one answer, but if you have additional questions, I'll be happy to answer them.