Considering that the SNP Policy is shifting day by day between "we will stay in the EU" (impossible) to "We will rejoin the EU" or "we will join EFTA/EEA) and now "don't know we will announce in time" I think it's abundantly clear it's a pretext. If EU membership was so critical there'd be nothing to debate.

But since over a third of SNP voters want to Leave the EU and Sturgeon doesn't want to alienate them there is.