And rule 0 of DnD is that the DM has final say.

So if the DM of your group agrees with the assertion that a lot of other birds that can speak can make those sounds so they should be able to as well, then that's the way it is at the table.

Remember the goal is to have fun, and sometimes some things will get bent a bit to have more fun. And if it's a flavor thing (like the bird people unable to say certain sounds) then I'm more inclined to change it for the table.

Like I said. Aarakocra are a fantasy race so what they can and can't say is a bit loosey goosey to begin with. Moreover, you are offering up a canonical description of them from a campaign from, what, 2nd edition? Here's something from 1st edition.

"You are the final arbiter of the rules" - Gary Gygax, 1st edition Dungeon Masters Guide.

3.5 Edition says:

"When everyone gathers around the table to play, you're in charge. That doesn't mean you can tell people what to do outside of the boundaries of the game, but it does mean that you're the final arbitrator of the rules within the game. Good players recognize that you have ultimate authority over the game mechanics, even superseding something in the rulebook."

5th edition Dugeon Masters guide says:

Your world is the setting for your campaign, the place where adventures happen. Even if you use an existing setting, such as the Forgotten Realms, it becomes yours as you set your adventures there, create characters to inhabit it, and make changes to it over the course of your campaign.

So canonical descriptions straight up do not matter. At all. But even if they did...

5th edition Aarakocra race page says:

Your character can speak, read, and write Common and one other language that you and your DM agree is appropriate for the character. The Player’s Handbook offers a list of languages to choose from. The DM is free to modify that list for a campaign.

The monster description also doesn't mention sounds that they make or limitations therein. There is literally no commentary anywhere in official 5th edition DnD that talks about aarakocra not being able to make those sounds.

'Canon descriptions' change drastically within the same edition, nevermind 30 years later. They also drastically change from source material to source material or it could even be homebrew, I never clarified whether it was or not. Even then, the Dungeon Masters guide explicity says to change things to your liking and to make a world that you like best. It is not just impossible to say what is and isn't pure canon but also just flagrantly wrong. It ignores the entire concept of Dungeons and Dragons and disregards every shred of creative freedom.

Finally, maybe you should try not to police or gatekeep peoples games in general but especially ones you're not playing in and are no part of in any way. Just some disgusting ass behavior.