Well, though the Aedui may have been occupied elsewhere, the insubres were still, part of the Aedui confederation.
With that type of logic, Rhodos shouldn't be part of the KH either, as it is doubtful wether the Spartans would have been able to send reinforcements, had they been invaded by the Seleucids, given that Pyrrhos was marching towards them in 272, and the Macedonians being as close as they were.
Still, such things happened...
Take, for instance, the Athenian expedition to sicily during the war with sparta, where they sent a fleet to support the small city of Segesta against the Syracusans, who were allied with the Spartans. The expedition failed, and in the end led to the Athenian defeat in the war, but such campaigns were sometimes undertaken.
The Gauls may not have had the same type of infrastructure the Romans had, but they were still capable of forming coalisions, such as the Aedui confederation, that were indeed a force to be reckoned with. Such Coalisions did also have the capability to make rather extensive campaigns. Also smaller tribes did have a rather complex organization for campaigning.
When they made a migrition in the 50's B.C, the Helvetii drew up lists of people and supplies for their march. The Aedui would probably have been able to do the same, had they decided to make a long distance campaign.
And, if I'm not mistaken, there were transalpine Gauls present at Telamon, so the Gauls were not limited to their direct tribal heartlands when it came to warfare.