GR translation: but def, after weeks of his snide comments?

[Mike Jing]

P130.15-22   Roger pulled over, and they watched the scuffed and dun
military going in to evensong. The wind smelled of fresh snow.
            “We ought to be home,” she said, after a bit, “it’s late.”
            “We could just pop in here for a moment.”
            Well, that surprised her, but def, after weeks of his
snide comments? His unbeliever’s annoyance with the others in Psi
Section he thought were out to drive him dotty as they were, and his
Scroogery growing as shopping days till Xmas dwindled—

What exactly does "but def" mean here?  Why is there a question mark
at the end of the sentence?