I was no where near "practically dry" until months later, but the sensation
you describe is something about which I am familiar.  I cannot tell you what
causes it, what stops it, or when it will happen again.  But, it seems to me
to be cyclic.  I'll be dry for long periods of time, gradually get worse,
then gradually get better again.  I can't tie it to stress, coffee, water,
walking or anything else.  For me, it just happens.

I think this happens to many of us.  I don't think it really means
anything changed.  It is just you've stopped being so careful about what
you do with time.   You wouldn't necessarily be conscious of these
things since most of them operate at a subconscious level.  Things that
can set it off are coughing, sudden changes of position, any kind of
pressure in the bowel, etc.

It may be worth checking with your urologist just to be sure.
Otherwise, start doing Kegels.   That may help some.  In any event it
may help your body learn to recognize precipitating factors.  Also,
remember that many older men without prostate cancer, and most older
women, have similar problems.  A few drops wetting your underwear is not
really that big a deal even though at times you may need to change
underwear more than once a day. I also quote the following old ditty,
which reflects the plight of older men, at times like this.   "No matter
how much you shake and dance, the last few drops go down your pants".

 My theory is that the only remaining shut off valve we are left with, kind
of fluctuates involuntarily due to many reasons. We've never been aware
because we always had it under control with the other valves we used to
have. Thinking of something sexy, will sometimes get me to relax and squirt
or dribble a bit.  I may be looking at my wife and thinking something nasty,
and whoops!