Only because Jacob Olofsson can’t do the tournament due to inury sucks for the habs

This is the best thing for Gus' development.

So I wonder where he'll go after the tournament ends cause coming back to the Jets wouldn't be good.

I’d imagine he stays in Sweden until his season ends over there, and then comes and plays for the Moose when he turns 20 (I don’t think he can play for them as a teenager).

Gustafsson would’ve been Sweden’s 1C even if Olofsson was healthy.

why not?
He's not from the CHL, he can play in the AHL at 18 like anyone else can.

IIHF rules say that European players can play in the AHL if they’re under 20 only if they’re 1st round picks Gustafsson was a second round pick.

Olofsson would have been #1, he’s a 1st center in the SHL

"Those basic requirements have held in place ever since. However, for young players signed out of Europe or collegiate players who give up their remaining NCAA eligibility in order to sign an NHL entry-level contract or AHL minor league contract, the minimum age to play in the AHL is 18.

For example, when the Flyers signed 2013 second-round pick Robert Hagg to an entry-level contract, he was 19 years old for most of his rookie season with the AHL’s Lehigh Valley Phantoms. Hagg was drafted from a Swedish team (Modo Hockey), so it was within the rules for the then-teenaged player to be assigned to the AHL."

The AHL does not care what their league says.
Their rules only make exception for the CHL.
If he is not under contract to play for another team. He is free to play in the AHL. As per the example of a 2nd round pick by the flyers above.