Can "Dear Humble" go together?. Requested further clarification please.

Hello,

I would like to a person wrote in a message to the senior aged person in iMessage to explain a scenario with polite and informal manner. Also to be noted that this person writing to one of his relatives.

The person wrote like this in the initial stages which caught my attention i.e. "Dear Humble Sir, the message goes on. "

Frankly speaking, I'm just literally puzzled with this form of English when written towards someone whether it's correct or not?.

Lastly, I do know this person in real life, the person itself is quite humble & polite when you speak directly. I don't see disrespect in any regards as well.

The only thing I manifested that the person is respecting and considering himself low in terms of importance when written to someone. Do I stand corrected in this regards? if not, Explain me further in a simple manner as I wish to understand in the clean format.

But for some odd reason, when written in this format, they are quite delighted & impressed by it as a matter of fact. It appears as a matter of perceptive & solely on your real life experience.

However, I hope to explain why I'm asking as I'm already bewildered by it in this state for the small thing but it matters me the most certain people are using at occasional times.

Thank you very much in advance and I sincerely appreciate your effort in explaining to me.