I think the reason that the strike was called was just poor judgment. Unite were trying to find a way out of this mess. Derek Simpson asked Willie Walsh for an extension to the strike mandate to allow the members to ballot on BA's final offer. WW agreed contingent on a no strike deal.
Len McClusky, seeing an opportunity to position himself as a union strong man prior to the election of General Secretary of Unite decided to announce strikes anyway. He also announced the BA offer would be put to crew, though not recommended.
Knowing that crew would probably accept the offer, McClusky gambled that Willie Walsh would let the process continue as the result of the consultative ballot "by electronic" means would be in prior to the strikes and so Mr McClusky could announce that the offer had been accepted. He would then have appeared to be both a Union strong man and also a reasonable negotiator. Unite walk away head held high as a union with BASSA intact and Len gets his boost for General Secretary.
Oops Len Misjudged horribly!