I think, already
and 
are questionable. is a kind of "please split me" - move. In the following, white gets a vulnerable small corner group and another group floating pointless in the center. Meanwhile, black can extend comfortably on upper and right side. Instead of you could have played Q15. This could yield the upper right side (maybe together with the black Q14 stone), however the upper right corner is then likely to become black. Therefore, I think that was already not optimal. I'm a complete noob if it comes to Joseki sequences but maybe attach at O17, settling the corner and then quickly play elsewhere (e.g. approach lower left) seems a possibility. At the end black is leading by about 80 points, thus the resignation seems unreasonable. Maybe he got an urgent phone call or his pizza was going to catch fire. Some people ("sandbaggers") like staying at low ranks in order to get easy wins.
is quite an advanced shape, I'm surprised an 11k played it. 8 is not so bad and after that 10 is the only move, but 12 should be the other push at o15 and complicated fighting will follow. After that 14, 16(?!), and 18 are all bad. So I would recommend for 8 you either tenuki (often a decent idea in unfamiliar corner situations) or simply defend the corner with r16 to make your corner safe and aim to split at p15 next so black should protect that somehow.