The 'Ba' puts this sentence in the conditional but doesn't seem to be covered in the tips & notes.
Got info from http://nualeargais.ie/gnag/kopul4.htm
"the copula exists only in 3 base forms:
- present tense (in part, at the same time the future) is
- preterite (same time imperfect, conditional) ba
- subjunctive (rare) gura