Maybe the service/food was just rubbish and he didn't want to have a confrontation in a foreign country in a foreign language?
Maybe the waiter was inept even if the food was brilliant and he didn't want to reward one example of inept service?
Maybe he just didn't have any more change?
Maybe he disagrees with the concept of tipping entirely?
Maybe he's just a tight-wad?
Who cares? Daily Mail trash to try to make him an enemy because he's rich and didn't tip. So what?
I tip when you do something for me beyond what I expect. Either you provide miraculous service, or you cope with a mistake / extreme busy times REALLY well, or the food is more wonderful than I expect, or even you're always open when other places are shut. Then I tip. Otherwise, you need to negotiate more pay with your employer yourself, not hope I'll stick 10% on the billed price. And even then, if I have no change, I don't want to faff about with notes, change, coinage, etc. to tell you that I want to give you a tip. I have a thing where I see it as impolite to let people KNOW I'm leaving a tip. It should be a surprise, a bonus, something unexpected. I don't even expect you to be grateful (or care if you are / are not) because I'm gone by the time you see what I've left (even if that's nothing).
A guaranteed way to LOSE a tip is to a) ask for one, b) include it on my bill automatically without consultation, c) express your expectation that I should give one (e.g. bellboys holding out their hand). I will instantly not give you any tip I was going to, for those. Did any of those happen?
My favourite gastro-pub (The Fishery in Elstree) provide wonderful service, even when busy. They are fabulously polite and attentive. The food is wonderful. They are open almost all day long. They make a BIG fuss when something goes wrong and work their nuts off to rectify it (down to almost-hounding the member of staff responsible quietly in a back room to check they've done every stage of everything else timely, so you can have no further reason to complain even if you wanted to). And whenever you pay by card they literally tell EVERY customer "just press Enter" when the device flashes up a message about if you want to add a gratuity (Enter skips adding one!). They don't dive on the table the second you leave scouring for your tip, or anything else to indicate that they expect one (I mean, they probably do half-expect one, but they absolutely do not show it and aren't offended if you don't - which I have done when I've not had the change to do it, but my regular custom more than makes up for it).
The pizza-delivery service near me that ALWAYS delivers a good pizza, hot, on-time, and without fuss get a tip almost every time they come to the door. Because they obviously care about keeping me as a customer and do an above-expectations job even on a very busy Friday night. The woman who was renting out a cottage in Cornwall to me and stayed open past 11pm especially for me to arrive? I tipped her on the final bill purely because she went above-and-beyond.
A tip is optional. Most people leave it for "not bad" service. I leave it for above-expectations service (considered long-term so a regular haunt like The Fishery usually see tips because of the way they can MAINTAIN that high level, rather than tips dipping over time because I *expect* it all the time I go in there, but even there I would leave no tip if there were bad service - I would expect it to be an indicator of just how good my service was that night). I have no problem asking people to remove service charges from the bill, or not leaving one at all.
Other people's financial considerations do not affect my payment for a meal, so that the waitress is poor or doesn't earn much or has to share tips doesn't factor in - I don't tip my airline pilots or stewardess or newsagent or the guy in the ticket office so why should I tip anyone else for just doing their job?
But when/if someone does something particularly special (even if that's just an exceptional display of good service), sure, I tip and don't mess about calculating percentages (how rude and thoughtless), I just keep rounding up until it seems enough.
Even if I was a billionaire, the same principle would apply. Exceed expectations, get something equally as unexpected. Do your job and provide the service as anyone else could? Well done (that's all).