I am well is correct hint not a direct meaning of the sentence "Mimi sijambo"
My clever linguistic explanation is as follows:
"Mimi sijambo" is the short form of "Mimi sina jambo"
In this context 'jambo' means a problem or trouble or difficult
Check number 2 below:
jambo nm (mambo) [li-/ya-] 1 matter, business, circumstances; 2 difficult, trouble: for example Miji imejaa mambo = towns/cities are full of troubles.
Mimi sijambo = Mimi sina jambo = I do not have a problem.
Greetings are part of the culture. Translations do not work, one should learn the usage. Sijambo is the answer of (american) How are you doing today, (English) how are you? . Dutch Hoi, or Dag, Kiswahili : Jambo. The only answer possible is: sijambo, with out the anglicistical mimi. Does not matter what state you are in: Ill, dying, celebrating. A next greeting is followed , like habari gani? Habari ya Kazi, etc. Greetings can exchanged for a long time, but never the actual information is given.
mimi is not used and is a mistake in the lessons. To read = Kusoma. I read nasoma. adding mimi is an Anglisisme which is grown because secondary school education is in English. Jambo is roughly : what is the matter. Sijambo all is ok. It is not common to tell the true state. Jambo is not well or unwell.