Good post OP. Spirit is basically code for lack of effort. If you're playing top level football, that's simply unacceptable, you live like kings, while people are scratching for pennies, you get cooks who make meals for you, perfect healthcare, everything is taken care of including your family and extended family. They just have one job - to play football. Sure there are lots of pressure to do well, but you can be sure Carlo knows when they have given enough effort or when they haven't. When I was playing high school and then afterwards socially futsal/indoor, losses killed me - everyone reacts different though. Maybe some of the players just didn't show like they cared enough.
Spirit also extends to a range of other things like trust. Even though it was a very attacking 11, the players selected should have been able to defend. It wasn't just the goal they let through, Newcastle had more corners, and they created more chances. That just means the players were strolling round the pitch. I doubt Carlo wants to put out such an offensive team again. Another thing is heart, these guys are given scouting reports on the opposition, given run downs and number of ways to beat Newcastle, they'd have to at least have 60-90mins of tactics before a game. They're probably also expected to watch tape. They're expected to be able to work out how to beat the opposition on the pitch, especially if you have more quality. If you can't work it out, then you shouldn't be on the pitch. By the looks of things they thought they'd beat Newcastle easily, judging by the complete waste of the 1st half.
And lastly spirit is also about working as a team. They just didn't, buildup play was pathetic, almost zero good chances created, and we saw everybody taking shots except DCL. He must be wondering what he has to do to get the ball so he can do his job.
Now its time for a reaction. Starts with proper training and focus and no BS. The transfer market isn't going to help either. Relying on one or two new guys to get the old squad out of the mess is unreasonable.