I disagree, but at the same time I also acknowledge that the rules are ambiguous and can be read in more than one way ;-)
If you are wielding one weapon then you can attack multiple targets if you are using a melee weapon (both SR5 and SR6). You can also attack two different targets if it is a firearm in BF mode (both SR5 and SR6) or three different targets if it is a firearm in SA mode (SR5 only) or up to ten different targets or even the same target more than once if it is a firearm in FA mode (SR6 only).
If you are wielding two weapons then you can attack twice (both SR5 and SR6). Nowhere in any of the two editions you mention do they say that you are not allowed to attack the same target with both your weapons at once. Quite the opposite actually:
SR6 p. 111 Multiple Attacks
Whether it’s shooting a bunch of bullets at multiple people, throwing shuriken at a marauding group, or using a sword in each hand, there may be times you want to deliver multiple attacks at once. This can be against multiple targets, or you could attempt two attacks against the same target. Whatever the case, to make multiple attacks, divide your attacking dice pool by the number of attacks made as evenly as possible, then make the rolls. If you are making two different kinds of attack (like, say, a gun in one hand, a knife in the other) divide each of your normal dice pools by two, rounded down. Defenders will defend as normal; if the multiple attacks are made against a single target, they only have to roll once, and their hits will be compared to all of the attacker’s rolls to determine success.
Also note that the action you use to combine with your attack action is called multiple Attacks (not multiple Targets).