If that were the case, why is there a need to disclose when he is the person at greater risk. Then I defer to points made earlier; it is a mutual decision and depending on what actually occured it seems difficult for me to presume to know who was actually at risk.
While unprotected receptive anal sex is the highest risk activity for HIV and most other STDs, the insertive partner is also at risk. The rectal lining can easily develop micro-tears that bleed enough to transmit the virus. Put another way, if an HIV+ man was always & truly exclusively "top" in both oral & anal sex, how did he get infected?