That's a bit of a stretch. Yes, there would need to be a dedicated team specifically for the passenger operations, but that team could be pretty small at first. The pair of tracks already exists, stations can be as simple as a platform and trailer, all the frieght companies already employ a huge marketing team. "Close enough that it is quicker than flying but too far to drive" - isn't the math as Brightline is proving. You can fly from Orlando to Miami, or you can drive, or take several bus lines... or you can take Brightline. People choose all options when given the choice.
I was trying to be succinct and witty, but if needed, I can expand on what I meant.
One thing I am assuming about a freight railroad starting passenger service is that they wouldn't just take a freight route (either with or without Amtrak service) and put some stations out and start passenger service. I mean, technically, they could do that, but it doesn't make sense from a business point of view. There are freight tracks, for example, between Kansas City and Denver, and theoretically a freight railroad could put stations along them. But the distances between those cities, the populations involved, and the population in the cities between them, are all factors that would make it hard to turn a profit.
So if a freight railroad wanted to make a profitable business out of passenger rail, they would need to pick two cities that were close enough, and had a high demand, but weren't currently served by any type of commuter rail or regional rail. Probably one or both would also be a tourist destination. This is, after all, what Brightline (or rather, the Fortress Investment Group) did.
Forming a public serving company involves a lot of complications. For example, ADA and safety compliance for passenger trains is going to involve a lot of review. A ticketing system and customer support are also necessary. I imagine a lot of lawyers and insurance are also necessary. And finally, a company needs to market itself. The Florida East Coast Railway didn't call itself the Florida East Coast Railway,, or the Fortress Investment Group, it called itself Brightline.
Another thing about Brightline is it has very nice stations. Which also takes time and money and is part of creating a good passenger experience. And also requires architecture, engineering, and lots of thoughts about safety and accessibility. Stations also need to be close to population centers. Many older stations are located in places that are no longer population centers.
So my point was: Union Pacific could look at a route like San Jose-Monterrey and decide to start a train oriented towards tourists, and they could actually probably make money at it, but by the time they are done with it, it is going to be called "The Dolphin", have new stations and probably at least some new tracks (and probably cross-ticketing and cross-promotion with Amtrak or airlines). I can picture a freight railroad doing that, but I don't think a freight railroad is going to just put out a platform in Wilson, Kansas and try to turn a profit.