Heavy Weaponry and Fighter Weapons Group

[Bardess]

Do heavy weaponry from the Technology Guide belong to a separate fighter weapon group, or are they in the firearms group? Since the required weapon proficiency is different, I’d say the first one is true.

[Melkiador]

I don't have the original source, but I'm afraid they don't belong to any fighter weapon group. I hope I'm wrong, but I don't think there is any requirement that a weapon must belong to one of those groups.

[Mysterious Stranger]

The only thing fighter weapons groups matter for is the fighters class feature weapon training. As such they are defined by the fighter class. the list of groups and the weapons in those groups can be found here. Anything not listed there is the GM's call unless the description of the weapon specifies otherwise.

I would treat them as their own group in a campaign I ran.

[Azothath]

to use & (somewhat) understand technological items PCs need the Technologist feat. That is outside of the normal weapon proficiencies.
Wizards can use Technomancy:D1, Bestow weapon proficieny:E2 for short term usage.

As mentioned existing RAW Weapon Groups do not encompass items from the Tech Gd. Thus it falls to the GM & homebrew.

[Azothath]

Proficiency: This entry lists whether the weapon is simple, martial, or exotic. If an existing weapon proficiency allows the new weapon’s use, that weapon proficiency is listed in parentheses. Note that Exotic Weapon Proficiency (heavy weaponry) works similarly to Exotic Weapon Proficiency (firearms) in that it allows access to a wide range of similar weapons.
Some GMs may wish to replace Weapon Proficiency (firearms) with Weapon Proficiency (technological firearms) to further restrict access to these devices to player characters in their campaigns. Technology Guide.
The supplement does not discuss "weapon groups".