I think Dinklage would be more offended at people tiptoeing around his height like it's a sensitive and embarrassing matter.
He knows he's short, we know he's short. He's not insecure he jokes all the time. It would be offensive if the joke was making fun at his appearance / height. It was more focused on the shield.
I thought it was just so silly when you suddenly see the guitar pick. Lighthearted joke.
I don't understand how this can be offensive unless you are looking for a reason to insult him.
An insulting joke would be more along the lines of comparing him to someone else or making fun of his shortcomings (lol) in a belittling way (that one was not intentional genuinely)
It's such a silly joke. It's not "omg hahaha look at how short he is" it's "omg hahaha that shield does look like a guitar pick now!" and then you imagine him 3cm tall and it's just an absurd image