Let's break Xanathar's!

[melvinmelon123]

You left out a part.

"...When you cast the spell, you can make a melee spell attack against a creature within 5 feet of the weapon. On a hit, the target takes force damage equal to 1d8 + your spellcasting ability modifier."

See the way it only targets one creature?
It's a melee spell attack yes, but regardless, the spell only ever targets one creature and doesn't have the range of "Self" in the description. It meets the pre-requisites for twinned spell.

For reference:

TWINNED SPELL
When you cast a spell that targets only one creature and
doesn't have a range of self, you can spend a number of
sorcery points equal to the spell's level to target a second
creature in range with the same spell (1 sorcery point if
the spell is a cantrip).

You aren't targeting a creature with the spell. You are creating a weapon within range. After you do that, you are allowed to make a melee spell attack with the weapon.