While I agree with you in spirit, there are two points to consider

1) it may have been unsolicited (you mentioned this), and 2) humans tend to be very "fuzzy". Maybe he should have towed the line, and now he's learned his lesson about why you always cover yourself.

But 99/100 times the human being on the other side just wants to get you the information you need and is just too trusting. We've all had those clients, and it's up to us to be trustworthy and not be the one who teaches that client what can happen if you don't protect yourself [1]

[1] Obviously what I mean by this is that you shouldn't be fucking over your client, educating them is another matter.