I'm not saying that the character is or isn't bipolar, but that statement is not true. Bipolar mood swings can certainly be triggered by environmental factors, albeit possibly to a lesser degree than in BPD. BP might have a genetic basis, but environmental triggers can affect swings. For example, a few hours of missed sleep can sometimes trigger a hypomanic episode in someone with BP.

http://psychcentral.com/lib/the-caus...ression/000912

Besides, diagnostic criteria are vague and sufficiently problematic that countless people are regularly misdiagnosed. I don't think it's possible to accurately diagnose a character in a movie based on less than an hour of total screentime anyway.