A 'transacting account' in my report is a Hive account that made at least one of the following transactions on the Hive blockchain: a vote, post, comment, transfer, power up or HBD conversion.
Splinterlands uses custom_json operations.
This post might be interesting to you:
https://hive.blog/hive-167922/@dalz/the-number-of-active-hive-accounts-is-growing-or-data-on-active-accounts-by-posting-curating-transfers-and-custom-json
That explains it, thanks.