if it was unintentional then no but if the in law has taken it wrongly then you may need to think about it
but not knowing what it is - it's hard to say
I asked (in our own kitchen) if a cup of tea -which was already poured by my daughter, was spare while the offended in-law put sweeteners in an adjacent cup. He had already explained the tea wasn't wanted for another family member. I hadn't paid much attention to that, so because he had to unnecessarily explain it again that's what upset him! -His back was to me ,but I saw clenched fists and dropped shoulders.....!
The worst thing about in-laws is that they are family so you can't just ignore them, but they're not blood relations so you can't really tell them to get a grip without causing upset!
if your in-law is "unintentionally irritated" by something as trivial as a cup of tea,.the cup of tea, is not the problem!.
(unless they are extremely petty!), something else is bothering this in-law, and they are looking for a reason to take offence.
IF you are looking for advise...ask them directly, what the issue is, NOT confrontationally, perhaps over a second cup of tea?....:-)
The person in question within the last year or so, has become fairly religious and shouldn't really behave like this. We don't meet all that often, but I'll maybe try to engage in conversation on a subject I know they have an interest in....