It is an interesting move
Recently came across this response to the NWALPA proposal, which appears to have some merit:
This unsolicited offer during contract negotiations very well could become NWALPA's last table position. If mgmt. were to turn this offer down, it would be very difficult for the union to retreat from this offer in full section 6 negotiations.
For instance, if the union were to open with a status quo contract, mgmt. could charge they were not negotiating in good faith as they'd previously shown a willingness to give at least half of the concessions mgmt. asked for. The labor board takes that very seriously.