The transaction counting in experience cards relies on counting Frontend transactions. This can also be Business Transactions and indeed in this integration, the left-most component seen to start the transaction was a Business Transaction component.
On further inspection, the Frontend metrics did show double counting of transactions. In particular, for one API call, there would be two consecutive responses logged in two separate 15-second intervals.
In this particular scenario, there were actually two copies of the script in the Enterprise Manager's scripts folder. As well as apim.js, there was a renamed script suggesting it was part of Precision API monitoring 3.2
Release : 10.7.0
Component : APM TEAM CENTER/ACC
Using Precision API Monitoring 3.4
The solution was to remove the duplicate apim.js file