Solipsism in the workplace

A colleague asked me to e-mail him a scanned copy of some hand-written notes that I had taken down during a discussion about a 'self-hedging yen loan' structure. At the end of the notes (and in reference to a particular consideration about the structure), I had written: [Solipsistic?]

He e-mailed me back to thank me for sending the scanned copy of the notes, and pithily added that he didn't think he was being solipsistic when expressing his view on that aspect of the structure.

I had to let him know that I had written it down because he'd used the word in conversation and I didn't actually know what it meant! I have since looked it up, broadly it means "to be of the view that one's own perceptions are the only things that can be known with certainty".

How this can (a) be applied to the taxation aspects of a loan idea, and (b) be taken as a slight, are personally quite hard to fathom.

Is it just basic animal instinct to expect to have to defend oneself on all occasions? Put another way, was it in-built for my colleague to assume [Solipsistic?] was a critical attack on him? Maybe - reducing it to a 'natural selection' theory basis, an animal suspicious of attack at all times seems more likely to survive than one who naturally assumes everything and everyone is benign.