"There are keys in the pocket."
Only in this case. に indicates a location but it does not say where at that location. It can be in, on, at, over, …
There is embroidery on the pocket.
There is embroidery inside the pocket.
are certainly different.
Some Japanese may pronounce /g/ as /ng/. It depends on the speaker and the region. Wikipedia discusses it: https://en.m.wikipedia.org/wiki/Japanese_phonology
If I remember correctly from reading other comment sections in the past (and I'm far from an expert)... It's a regional thing, so some people in Japan will pronounce their 'g's like that, while others won't.
That would mean that someone has put the keys in the pocket for a purpose.
I tried writing カギ in kanji (鍵), and got marked wrong. I'm guessing it being written in katakana is more common. Still, I don't see why I should be marked wrong for that. Reporting.