Leaving food and scraps lying around is well known to attract pests, so I don't blame the agent for ticking you off to be honest.
Did someone sound the klaxon horn for the obsessionally tidy ? This thread is going to go off topic soon, I suspect and become a housework rant.
It's a professional not parental inspection.
It is a PROPERTY inspection. NOT a housework inspection.
The letting agent had absolutely no business commenting on the dishes in the kitchen sink or any other aspects of housework.
A PP has already summed up a good response. I think it was something like, 'thank you for confirming that all is in order with the property I rent.' Please be advised that I have withdrawn my consent for any future unsupervised PROPERTY inspections of my home.
Do not comment on how rude they are to comment on your lifestyle i.e. a few dishes and pans that will get washed up when you come home from the work that you do to earn the money to pay the rent.
If you ever go into the agent's office. Pointedly look at any coffee cups etc that might be on their desks. Or ask, 'I guess the kitchen in this workplace must be spotless, eh ?'
Never forget you are a tenant and as such have legal rights. You are not a house sitter. You do not pay rent as a favour.
Do not, as tempting as it is, start your correspondence with:
Dear Cheeky Bastard