That is how the "slash mention" currently works. There's this idea asking for what you're thinking it should do.
I did see this workaround suggested by a comment in the idea
Create a dedicated Chatter Group and then @tag the group instead of another record. Groups do have a related Records list
That workaround only works if that fits your use case (a group flagging records for some purpose). It doesn't seem to meet your need in terms of ideal experience as sales user would have to go to a record and then tag the sales group.
In terms of a custom/programmatic workaround, you're left with having to use the Connect API which means, for apex, you'd have to look into using ConnectAPIHelper once it's been posted to copy it to the record's feed. I wouldn't recommend this approach, but it's possible (details below)
Within the Connect API, you can get the MessageSegments within the feed elements and it contains a ConnectApi.EntityLinkSegment which has a ConnectApi.Reference that has the
Id to the record where you could then copy the contents and post to the record's feed. Problem is, within the FeedItem trigger or even querying it in a scheduled apex, the body doesn't return as ConnectApiHelper expects so you need to rely on ConnectApi.ChatterFeeds.getFeedElement().