I think this explanation is as likely if not more so than any other, no advertising better than free advertising!
You never know this could just have been a clever marketing ploy by Tesco.
I can just imagine the VP of Marketing saying something like, "Stick the wrong cow in our posters and let's see how much media coverage our new milk promotion gets! Best of all it is all free!"
7DII+Grip, 7D+Grip, 40D+Grip, 5D+Grip, EF 24-105 f4L EF-S 17-85, EF-S 10-22, EF 70-200 f2.8 L IS II, EF 2x III, EF 100-400 f/4.5-5.6l IS II, Σ17-70 f2.8-4 C, EF 50mm f1.8, 550EX, Triopo TR-985, Filters Remotes Macro tubes Tripod heads etc!
5D, 20D, 24-105, BG-E4, BG-E2N, 17-85, Nifty 50 pre owned.