Little did I know that the great Mahāthera was to make the tea himself for us! I was stunned by such humility.
I was myself stunned by this sentence, since making tea for a guest is certainly something quite normal in my world, and not a particular sign of humility.
In Christian religion even the Pope makes a big show of humility, for example by washing and kissing criminals feet:
This seems very far apart from Theravada Buddhism as currently practiced, where it’s more like the lay people and junior monks who wash the feet of the ‘Ajahns’.
So how was humility understood in EBT? And was it recommended? Also to monks?
I hope it is welcome to note that I have a really warm fondness for your questions. Anyway, here’s my 1 minute attempt at answering a couple aspects of your Q.
Often in human culture, the significance of things is in the meanings built up around particular contexts, and the actions themselves have no inherent meaning.
When I use the following example, I’m not drawing any other likeness then to highlight how context may colour meaning… while tea making is, indeed, a totally normal thing would you not even bat an eye lid if you went round to Buckingham Palace and the queen herself made you a cup of tea?
Naturally the queen has accrued her ‘status’ by a totally different system of values to that of Ajahn Brahm, but guess a point they have in common is that for their different reasons they are so highly revered that they don’t ever have to make a cup of tea if they don’t want to (as so many are desperate to do it for them). When they do so anyway, it might be reasonably taken as some light-hearted indicator of how they themselves relate to privileges available to them.
The Buddha washed his own feet (eg. SN4.7) and also washed up after a monk who had soiled himself (Kd8).
that’s a cool comparison and makes things clearer thanks! Though for me it’s more someone like say Gustavo Dudamel who is a hero for me (btw a lot of musicians in his orchestra were Soka members), and indeed I would be honored - if not stunned - if he made tea for me
In the larger sense (as in beyond the necessary constraints of a forum), I think your questions are totally on topic! One of the suttas that allowed me to feel a little safer exploring Buddhism when I first arrived at it’s door was MN47. It and a few others gave me confidence that this is a teaching most absolutely about inquiry. This was just as well for me, because my orientation is to attempt to rip a thing to shreds and if something is left standing afterwards then perhaps consider it trustworthy. That said, I was glad that I was only interested in doing a delicate, careful, peaceful ripping to shreds attempt; not least because I intuitively had a sense that this teaching goes well beyond the intellect.
Much metta.
Your question is not trivial as it questions current customs. I would distinguish three frameworks: 1. monastics & laypeople 2. senior monastics and their junior monastic students 3. humility as a general value in ‘Buddhism’.
to 1. even if the EBTs attitudes are all over the place I’d say the original position was quite clear: with leaving the householder life monastics were supposed to leave all considerations of praise and blame, high and low status behind. If you praise or blame is up to you, the lay person - the monastic is following dhamma-vinaya and that’s it. A monastic expecting laypeople to behave in a certain respectful way beyond normal courtesy is full of themselves and their social persona. (A CEO or politician etc. of course as well, but they don’t pretend to have left the social game behind).
to 2. Here a junior monastic directs their faith and devotion to a teacher who represents the highest goal. In this case the position of humility towards the teacher is self-chosen, and I would argue, necessary.
to 3. I’m actually not sure about this one. I’d say the EBT position is ‘do your job in a kind way’. The texts certainly don’t expect a king to be humble towards his subjects or a householder towards his slaves. Rather, ‘don’t mistreat them’, ‘be kind’, but also ‘know your place’. (?)
and your tolerance when my curiosity leads me a bit off topic sometimes! 
With metta 