That's garlic you harvested last year, right?

Not sure when you harvest in San Francisco, but for me in VA, we harvest in June, so my bulbs have been sitting around for 10 months. Mine has been pushing out new "sprouts" for months. I just use the ones that are growing sprouts first and save the rest for later.

So to answer your question, what causes this is time. Garlic, onions, and potatoes will all start growing if you leave them long enough.

OK. Now I get it. Those are last years galics ?
The one that has fully opened, probably was overdue when harvested OR just the sprouting pressure pushe the wraps open b'c there was not enough wrap on it to begin with. JMO