The Account Records in question are Type-5 “LINK Journal” Account Records, as opposed to LOGON or other usage Account Type Records.
Although it's not clearly stated in the format of the Type-5 Account Record (columns 9-16 = Account Number), the Account Number is that of the user that owns the minidisk that is being linked to, not the user that is doing the LINK.
The setting of the HiDRO default option ACCOUNT does change this. The ACCOUNT setting (ON or OFF) is referenced in the HiDRO MODULE (there is no flag set in the HiDRO code for this). This default is only stored in the HIDRO CONTROL file.
When a job is submitted, SYSBSHELL sets up the job environment. Part of that processing reads the HIDRO CONTROL file. If the setting for ACCOUNT is set to ON, this causes SYBSHELL to call an external HiDRO supplied routine (SYBACT) that issues a Diagnose x'4C' with sub-function x'0000' to set Account Record generation to the "Requesting UserID" (the UserID that submitted the job). The intent here is that the submitter of the job will be "charged" for the resources used for that job.