The main thing is that the first overtake happened on lap 20 – which I think was before Red Bull had a moan to race direction about cars going all four wheels off track there, despite the drivers being told that there were no track limits being policed at that corner in the pre-event briefing.
The race directors then decided that track limits were now being enforced there (because Red Bull had a moan, I suspect) this was evidenced by a message to Hamilton telling him to stop running wide there, he responded to the effect of “but they told us it was fine” to be told “yup, we know, but the rules have changed”, so he stopped going wide there.
Verstappen then overtook him with all four wheels off of the track at the exact spot where they’d been specifically told not to – in fact the exact spot that Red Bull had complained about Hamilton doing exactly that.
Skip onto Imola where track limits didn’t need to be enforced, as the design of the track itself does quite a good job of enforcing them(!) and Hamilton got very lucky with the red flag for Bottas/Russell negating his off, allowing him to finish second (mentioned by Horner after Portimao)
Followed by Portimao, where track limits were being enforced more strictly (I think it was “all four wheels onto the green painted bits” and you were considered offtrack anywhere) and Verstappen ran off track twice at critical points, causing him to miss out on pole and lose his fastest lap.
Horner’s Imola comments are obfuscation, as Hamilton was massively lucky, the rest of the complaint is proper sour grapes, as Red Bull have been tripped up three times by their star driver not being able to keep his driving within the defined bounds of the track – bounds which they themselves pushed for tighter regulation of, as they believed it would give them an advantage!
While track limits is a ballache, and should be policed consistently all the time, Red Bull can get in the sea about this, as they’ve fallen victim to it actually being consistent!
Rant Over.