Did I understand well?

Question

FULL EXTRACT

"Ah, Mr. Roberts, I trust you are not one of those business men, who make a business of never having to do with unfortunates. For God's sake don't leave me. I have something on my heart--on my heart. Under deplorable circumstances thrown among strangers, utter strangers. I want a friend in whom I may confide. Yours, Mr. Roberts, is almost the first known face I've seen for many weeks."

"It was so sudden an outburst; the interview offered such a contrast to the scene around, that the merchant, though not used to be very indiscreet, yet, being not entirely inhumane, remained not entirely unmoved."

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Did I understand well?

It was so sudden an outburst; the interview offered such a contrast to the scene around, that the merchant, though not used to be very indiscreet[=used to be little indiscreet], yet, being not entirely inhumane[=being a little humane], remained not entirely unmoved.

Answer 1

I think the phrase could translate as 'not accustomed to being very indiscreet' - that is he was usually pretty discreet.  He's saying he's a well mannered person, discreet, humane and capable of being moved by such an appeal as he's hearing.

I vaguely recognise this quotation - perhaps we could know where it's from