Obviously ridiculous, but the rules don't specify that you have to be able to shift a "moveable obstruction" by yourself.
Speith worked the rulebook perfectly at Birkdale, it's every pro players job to know the rules inside out. The one thing that day that was wrong imo was that the driving range should have been OB.
I know I said we would be calling Bob's drop utter BS if he wasn't Scottish, but I've never said he was wrong to use the rules properly. It was a huge stroke of luck, but he still had to hit a stunning shot and sink the putt to take advantage of it.
There are lots of questionable drops every year, worst one this year IMO was Schauffele claiming line of sight relief from an object that was impossible for him to hit from where he was. A clear window to hit a punch shot to the green my arse.
Read a couple of things online suggesting that at more modern courses sprinklers in the rough might be quite common. Apparently it's standard practice to fit them to make sure there is enough water to get the rough to grow quickly, rather than just leave it to nature. Once the rough is established they just never use them again.