What caused auto fill?

I’m helping my 3rd grader and out of the blue, when he uses ‘text box’ and types a letter it changes it to a word. For example: when he types the letter “y” it changes to “and”, when he types the letter “z” it changes to the word “with”. I’m completely stumped !

I’m wondering if his computer is set up for a foreign language user. If so, he could go to computer settings, language and then change the language. Or go to settings, spelling typing keyboard then click typing. Now click typing and shut off text suggestions. I hope that helps.