Mandatory Seinfeld reference [1]. Honestly, this is good advice. So much of work is actually just perception management. Looking annoyed or angry without actually being mean or inconsiderate is a bit of a cheat code.
Beyond perception management there's the issue of avoiding unnecessary interruptions. It can be hard to define what's necesary and what isn't. Rarely does it have anything to do with what someone is interrupting you for but instead, it is (once again) it's perception management.
There is a context-switching contest that comes from being interrupted and it can be hard to get back in the zone. So you want to avoid people interrupting you to ask something that would quite literally be the first link on a trivial Google search.