"Bad finishing" takes due credit away from good defending. So this illustrates the exact flaw with xG I mentioned earlier.
35-40 shots, high xG...sure. But now tell me if every time Spain shot, was it the inherent weakness of their shot that resulted in no goal OR was it the striker being forced into an awkward angle/rushed shot/awkward physical position by an excellent defender that caused no goal to be scored?
xG doesn't make that distinction.
So Cape Verde may have defended excellently to force that draw (rather than Spain making errors in front of goal) and a brilliant defensive team is just as praiseworthy as a brilliant offensive team. In fact, brilliant defenses often win tournaments! Italy, Germany traditionally typify this approach to tournament football.
I do have my opinions on why Spain didn't win that match and I feel it was fundamentally due to unavailability of star players and heroic CV defending rather than any errors by Spain in front of goal. In other words, credit is due to Cape Verde!
Iran today were quite similar - they forced Belgium to scuff shots and/or not have a clear route to goal and their goalie did the rest.
Btw, xG for Spain in that game was 2.03 and for Belgium today was 1.82, which isn't a huge difference. Both games played out similarly even if one looks at just the stats.