That's exactly why he did it. He's a nasty, vindictive, racist colonialist.
I'm just saying that if he's as smart as people claim, if the whole bumbling idiot is a calculated act, then there's not much to benefit from idiotically reciting that poem, it's not like there's some vast constituency in the British public who love The Road to Mandalay. It's an obscure reference, most British people have never heard of the poem... He seemed genuinely surprised that he shouldn't recite the poem.
I think the bumbling idiot thing is genuine. That doesn't also exclude him from being a nasty vindictive racist colonialist.
The nice thing about it, is it's a spectrum. If you're in the conservative-intellectual bracket, you still probably enjoy the provocation of the politically correct, and the imperial nostalgia stuff. If you're in the conservative-middle-brow bracket, you still feel good about the fact that your racism is being associated with Great British poetry.
I don't think he's a genius, or that he's playing fifth-dimensional chess, or something. I think it's just an advantage of this whole bumbling persona - that he can go to events like this and basically do what he wants. So when he thinks up some kind of stunt - like reciting a colonialist poem, or getting stuck on a rope, or whatever - he can go ahead with it, because it fits with his image. That gives him a whole range of communicative strategies most politicians don't have. What he actually communicates (the blend of dogwhistle racism and attention-seeking) is actually pretty normal.