That is the Cardinality of the TagCategory.
Since we didn't specify it, it defaults to Single.
The other option for cardinality is Multiple, see the New-TagCategory cmdlet.
It will suffice to just add -Cardinality Multiple on the New-TagCategory cmdlet in the script
You can change the existing Tag Categories with the Set-TagCategory cmdlet.
Blog: lucd.info Twitter: @LucD22 Co-author PowerCLI Reference