Creature Size Tag
 

For some reason the size tag for creatures is set to have multiple tags assigned. Is there a reason that I'm missing or is this an oops that needs fixed so only one can be selected?

If I had to guess, I'd say it is designed to allow for entries where a creature can appear in multiple sizes. Some of the 3E stat blocks were like that, so I'd guess Pathfinder might do the same. I don't think I've seen it yet in 5E (unless a RW user were to include various ages of dragons in a single topic/article), but might as well keep the options open.

That sounds logical.