I think if your baby is hungry, and just getting a few mouthfuls of baby rice, at pretty much 5mths, that's absolutely fine. You know your own baby.
And, if GP advised, he/she also perhaps think your baby looks developmentally at that stage too? And going by what you have discussed with them.
I think comments like "please stop feeding your baby" are a little too scare-inducing, and if it was me would make me feel like I had been poisoning my child or something.
FWIW I started with just baby rice for both mine, for a good 3/4weeks. Both big babies, both hungry babies, both getting mooooore than enough milk, they were starting to grab at my spoon and watch me eat, plus I needed a way to satisfy them and keep them full. Plus, they both took to it very easily and loved food from the start. 3day rule is brilliant as far as I am concerned, and certainly produced no weird behaviour with food.
Keep away from the meat and protein until it is recommended and needed in their diet though, if for nothing else other than to save you from the unbearably stinking nappies! + all health reasons of course....