The dialogue is invented, but the insights ring true. Seneca had always defended the gravitas of the principate, keeping Nero out of chariots and off the stages of theaters. Octavia, with her sober bearing and high birth, represented the same gravitas, especially by contrast with Poppaea. Seneca is bound to have stuck by her, but doing so put him on the same side as the ghost of Agrippina. Nero had already shucked off his mother; he was done listening to his surrogate father as well. And that spelled danger for his beleaguered wife.
