Passport stamp

Don't worry, passport stamps can be on any page. The date on the stamp shows its validity, not what page its on.

Don't worry about it. All is well.

"Why did he do this and do stamps need to be in order? "

It seems that some of the immigration officials (in many countries) deliberately pick an "empty" page, as far from other stamps as possible., At least, when I see them leaf through my passport very deliberately, and pass by perfectly good empty spaces to get to a totally unused page, that's sure what they seem to be doing.

Fortunately, it does not matter at all. As long as the stamp is there, you're good.

No, they don't need to be in order. I have Ukraine stamps sitting right in the middle of my otherwise empty passport.

You'll get your Schengen exit stamp on the same page as the entry stamp from Kraków. Should you re-enter Schengen in the future, you most probably get a stamp on the same page as the Kraków stamp (if there is still space) or a page close to it. They do that on purpose so that Schengen immigration can easily find them and have all the entry and exit dates on one page. London is not in Schengen, so that stamp is totally irrelevant.

The Schengen Area checks passports, and stamps them if you are from outside the EU, on both entry and exit.
The UK only has checks (and stamps if needed) on entry. On exit they rely on the transport company informing them, which they are required to do by law. THis is why you haven't got an exit stamp from the EU.

The only issue with random stamping is some places require a blank page, which if everybody stamps on a different page may be a problem.