 in the first place. It's not at all clear how a gas giant formed under those conditions.
There have been some hints that giant planets can form much like stars do, from the direct collapse of a gas cloud. But these tend to be super-Jupiters, objects that are closer to a brown dwarf star than they are to Jupiter. So it's doubtful that they're relevant to this system.
It's worth remembering that there are two other Jupiter-class planets that also orbit M-dwarf stars. So any solution we arrive at to explain NGTS-1b should be general enough to account for these other cases, too.
Which is probably why the authors of the paper argue that it's best to understand the full extent of the problem first. To do that, we'd want a survey of dwarf stars to get a sense of how frequently they host gas giants. From there, we can start determining the conditions, like heavy element content, that are associated with gas giant formation. With that data in hand, it might be possible to update our models of planet formation to account for these unexpected systems.