I've only been married a few months short of 5 years now, so please don't take this like I'm some expert...
Marriage is all about trust and respect. Buying expensive stuff behind a spouse's back violates that IMO. I'd be pretty pissed if my wife spent that much money on ANYTHING without my knowledge and consent. She'd be equally upset if I did it, and for good reason.
The way I look at it, if you have to hide it, you shouldn't be doing it. If you can't discuss it like a family is supposed to do, it's pretty safe to say you're doing something wrong.
That system doesn't exactly cost pocket change.
If it's more than $100 or so, my wife knows exactly what I bought. She may roll her eyes and not truly get it, but she knows. That works both ways.
That's not her being the boss, nor is it me being in charge. It's not asking permission to buy a toy. It's called respect for one another. She's never said I can't buy anything. I've never told her she can't. We have reminded each other once or twice that the money for a toy would be better put towards a necessity. That's being adults.
I'm not trying to bash the guy. I don't know him nor the entire story. I'm not trying to justify the lady's response, as I don't know her nor the whole story either. I'm saying what I'm saying because threads like these seem to pop up all the time on forums.
In s nutshell, unless she's asking if the jeans make her ass look fat, honesty is the best policy.
Footnote - My wife never asked about the jeans. But I learned my lesson time and again during my bachelor days. One response came to mind on s few occasions - it's not the jeans that make you look fat.