Did some Google searching myself:

The JWT stands for Jönköping Westra Tändstickfabrik, one of the major matchstick factories in Sweden before they consolidated into the Zyn company.

https://thoresmatches.se/tandsticksfabriker/jonkopings_westra_tandsticksfabrik.htm

You can see in the matchbox pixtures in the page above, that they did use the term "impregnerade" to refer to their chemical treatment on the matchsticks.

This article says that the impregnation treatment was beneficial because it made matches blow out quickly without smoldering:

https://thoresmatches.se/tandsticksfabriker/sakerhetstandstickan.htm

This post on the SomethingAwful forums seems to show an original photo of the match boxes, posted by someone with a Swedish username.

https://forums.somethingawful.com/showthread.php?threadid=3948652&pagenumber=9#post521474833

These matches don't seem to be recorded in many museums, so probably either a modern gag, a period knock-off, or genuinely a Swedish person who didn't realize that impregnerade had a double meaning in English.

There is a matchstick museum in Jönköping, Sweden that could probably answer.