Tom Holland has built something of a reputation as a guy with a tendency to say more than he should about the Marvel Cinematic Universe. It appears that in order to keep him quiet Marvel has hired Benedict Cumberbatch as a Spider-Man wrangler. The two actors have been doing a lot of media appearances together, and it seems the reason why may be that Cumberbatch is good at getting Holland to shut his mouth. Check out this hilarious montage of the Doctor Strange actor cutting of Holland before he can get himself in trouble.
To be fair, talking to the press while not talking about the things you're not supposed to talk about has to be a difficult skill to acquire, and Tom Holland clearly hasn't figured it out yet. Thus Benedict Cumberbatch has to jump in to answer questions, bleep Holland's words, or in the best part of the iamgeekingout montage, literally start singing over the guy in order to keep him from saying something he's not supposed to.
Keeping secrets is the name of the game with franchise filmmaking these days as it's vitally important that spoilers not be revealed before the audience has a chance to see the movie. For the most part, the studios do a pretty good job of keeping things orderly, but at the end of the day the actors are people and people can make mistakes, meaning you can never be too sure what somebody might accidentally say.
One gets the distinct impression that most of the rest of the Avengers: Infinity War cast was told that if they find themselves doing interviews with Tom Holland, to keep an eye on him. Either that or the reason we see Holland and Benedict Cumberbatch together frequently is because he has this special skill.
It's a tough balancing act because you want to give the media something to write that fans will enjoy reading, so not saying anything at all isn't really an option. At the same time, you do need to be careful not to reveal too much. I'm guessing that with a bit more practice Tom Holland will get the hang of things and before long he'll be the guy cutting off some other MCU newbie down the road. Holland is pretty new to this whole game, it just takes time.