Wasn't the length of the handshake...but the assertive tug of war Trump played while doing it.
Many times that is seen as a bid to assert dominance or control over someone. The "I'm stronger than you, or I'm running this show."
Yes, it definitely could be construed that way. In reading, found it's apparently well known Trump is a person who prefers to not shake hands, had been quoted as calling it barbaric, so before his campaign probably got away with not doing it. Some sources claim germaphobia, but regardless the reason, this isn't the first instance of this behavior. Saw an article with a few examples of his horrible handshake, pumping back and forth instead of up and down, jerking and twisting people arms into odd positions, and one would think someone would have discussed this with him some time ago because it's considered rude. It may be an awkward display of his own personal discomfort, or some weird power play he does on purpose. Either way, it seems it's a social skill he could use some guidance and training.