I believe it's a continuity error, based on this quote from JMS:
About Sheridan asking the Roanoke to surrender
Yeah...the reference was kafuffled. There was so much going on, so many EFX shots, so much rearranging of shots to make everything work (we literally delivered this 2 hours before the process for uplinking started) that this slipped past. I'll assume that Sheridan got excited and said the wrong name. It'd happen to anyone. Right? Right?
This is documented on the Lurker's Guide page for Severed Dreams
To clarify - as @Radhil points out in the comments - the EFX were the error here; the dialogue of Severed Dreams and Intersections in Real Time would be coherent if the EFX actually showed the Agrippa (not Roanoke) being rammed at 33:10 and the Roanoke (not Agrippa) being hit at 34:09 and then destroyed as a result. The fact that the shot was labeled Agrippa and not Roanoke wastwo shots were cross-labeled were the "kafuffled reference."
This is more easily understood if you're familiar with JMS's habits - whenever he blames or attributes something to a character in the manner he does here ("Sheridan got excited and said the wrong name"), he's actually indicating that the "real world" (JMS, producer, director, EFX, somebody) screwed up and is using the tongue-in-cheek humor of blaming the characters to excuse it. If you read through the various quotes collected in the Lurker's Guide, you'll see it - when he describes actions by an actor, he's straight up. When he describes actions by a character, then he's either imparting a deep philosophical understanding of the story or hanging a real-world snafu on them.