Weird garlic

I pulled up my remaining garlic today. As an aside - first time I've grown Iberian Whyte and they're fabulous bulbs, biggest I've ever grown. And it's not the conditions or environmental, because they were right next to the Marco garlic, which has all come out rather small. And they might have even grown a bit more if I'd left them in, because the leaves were still green though lying down, but I needed the space.

But my question is - one of the bulbs was a bit weird, never seen it before. The bulb itself is normal, but about an inch up the stem there's what looks like another little garlic bulb growing inside the stem, separate cloves and all. Anybody know what this is and what causes it?

I asked this last year also, the little bulbules won't be very edible as they're quite stringy, bit like they've gone to seed - think it may have something to do with dry hot weather at the wrong time? This year mine have got rust instead for a change