I might be thinking ~ inside, but I wouldn't actually say that out loud.
What I think and what I say are two different things.
ご質問ありがとうございます。
① "I might be thinking ~ inside,"=「内心、~と思っているかもしれない」
"but I wouldn't actually say that out loud."=「でも、それは実際に声には出さない。」
② "What I think and what I say are two different things."=「思うこと、そして言うことは異なることです。」
ご参考に。