One thing is that this latest Buttigieg surge is that he initially gained only ~1 point or so after last month's debate, but the media declared it was a huge surge ... and now he's seemingly having a more significant surge, at least in the early states.
Some evidence of this: Buttigieg's net favorability numbers, though they were already quite good, didn't actually improve in this poll from Monmonth's previous one. He's just been more salient in the conversation so more voters have him as their first choice. 
p.s. This is a bit of the risk candidates face in attacking Buttigieg. They potentially elevate his profile and keep him in the news. You don't face that problem as much when attacking Biden, Sanders or Warren since they're already household names.
