If I text my boyfriend "what's up?" And he says "thinking." Does that mean he's upset?

My boyfriend and I were texting and he was giving short vague responses which is how he always texts anyways but I couldn't keep the conversation rolling so I said, "sooo whatcha up to?" And he said "thinking" so I asked, "what are you thinking about?" And his response was "just life" 🙃🙃 is he upset? If so why isn't he telling me straight up that he's upset. If he's not upset though, why is he sending me these vague texts? We've been dating for 4 years and he does this a lot but I've never been able to figure out why.
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Just found out he was upset. So would y'all consider this type of response to be reasonable or hella passive aggressive? I hate having to pry answers out of him
If I text my boyfriend "what's up?" And he says "thinking." Does that mean he's upset?
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